Leopard geckos at Petco are around 20 dollars. BUT I would not recommend getting any reptiles from a large chain petstore like Petco or Petsmart. They *usually* do not treat their animals right. Try a rescue/shelter or REPUTABLE breeder instead.
Here's a care sheet I wrote a little while ago. It's not perfect and there are a couple things missing but it should definitely get you started. It was written based on my personal experience and tons of research. If you have any questions about it please ask me.
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Housing ~
Finding a good enclosure for your leopard gecko is very important; it is what they will spend their whole lives in.
Housing Leopard Geckos Together:
Leopard geckos are solitary animals by nature. Males should never be housed together under any circumstances, as they will fight. Females will get along nicely given they are provided with adequate space (addressed below). Make sure whatever leos you house together are introduced as hatchlings (under 3 months of age), preferably, or as juveniles, or under one year of age. Prepare to separate the geckos if any major fighting occurs, but the occasional light squabble or disagreement is to be expected, especially as the leos are establishing the dominant and the submissive animal in the relationship.
Type of Enclosure:
There are many kinds of enclosures you can choose from when housing leopard geckos. The most common enclosures used are glass aquariums. Vivariums with mesh metal screens all around are acceptable as well. WHICHEVER ENCLOSURE YOU CHOOSE MUST BE LONGER THAN IT IS TALL, since leopard geckos are terrestrial (ground-dwelling) lizards. They can not climb, and they can hurt themselves if they try--and try they will.
Size Requirements:
There are various opinions on what should be the minimum tank size for leopard geckos. Some say that 10 gallons is suitable for one or two geckos, while others argue that 20 gallons is the minimum for one gecko. Perhaps the most agreeable and realistic size minimum is 10 gallons per leo. Putting two leos in one 10 gallon tank will most likely result in fights over territory. 20 gallons is more than enough for one gecko, as they are not incredibly active lizards and spend a lot of their time resting in a hide. If you are using an enclosure other than a glass tank the size minimum for one leopard gecko is about 20 inches long by 10 inches wide and 10 inches tall, or about 50 x 25 x 25 cm.
Substrate ~
The substrate that you use for your leopard gecko is the material that is used on the floor of the vivarium. It collects feces and urates and is what they spend all of their time walking, eating, and sleeping on.
Loose Substrates:
Sands, wood chips, moss, corn cob, walnut shells, and other loose substrates should be avoided at all costs since they are very risky. Consumption of the substrate by the gecko will result in impaction, or a blockage of the intestines. Wood shavings are especially harmful as they are rough on the leo’s delicate skin and can harbor bacteria.
Mimicking their Natural Habitat:
Some justify using sand as substrate for leopard geckos by stating that it mimics their natural habitat, since they are desert animals. This is not true at all. These geckos do come from the desert, but not the kind with yellow sand blowing around and sand dunes everywhere. Leopard geckos come from the deserts of Pakistan and Afghanistan. A simple Google search of the terrain of these areas shows that they consist of hard-packed dirt, stone, and sparse vegetation. There is hardly a risk of impaction for these lizards when living in the wild because the sand and dirt is tightly packed into the ground, rather than the loose sand sold and used as substrate.
The Best Substrates:
This is why I strongly recommend using stone tiles such as vinyl, ceramic, or slate as substrate for your gecko. They are attractive looking, inexpensive, 100% safe for the leo, and help recreate their natural habitat. I would say that tiles are the best possible substrate for leopard geckos. Paper towels and week old newspapers are great substrates as well, being inexpensive, comfortable, easily removed and replaced, and completely safe. They are unnatural, but still a great choice, especially for those on a budget.
A Word on Reptile Carpet:
Reptile carpet is not the worst substrate out there, but I still do not recommend it. The small fibers that stick out of it easily catch toes, nails, and even teeth. Like wood shavings, it harbors bacteria and is unsanitary. Not to mention it is unattractive looking (in my opinion, at least) and unnatural. There are other substrates than you can use that are a lot better and less risky than reptile carpet.
Hides ~
The “hides” in the enclosure are the areas that your gecko will retreat to during the day when it is sleeping or whenever it wants shade or security. These can be anything from cut up tissue boxes, empty cottage or cream cheese containers, paper towel tubes, Tupperware containers, reptile decoration hides from a pet store, and more. You need a minimum of three hides per leo in the vivarium—a cool hide, warm hide, and moist hide.
Cool and Warm Hides:
You will need one hide on the cool side of the vivarium. The gecko will retreat to this hide whenever they get hot on the warm side and need to cool down. You will also need one hide on the warm side of the vivarium, over the under tank heater. The gecko will most likely spend most of its resting time in this hide as they are cold blooded and need the warmth, or they will not be able to digest their food—which can lead to impaction.
Humid/Moist Hide:
The humid hide should be placed either in the center of the vivarium (if you are using an overhead heat lamp or light to supplement the UTH) or on the warm side (if you are jut using the UTH, and not using an overhead heat lamp or light). Fill this hide with warm, damp paper towels, cypress mulch, coconut fiber, orchid bark, perlite, peat aka sphagnum moss, or vermiculite. Make sure to spray the bedding with warm, clean water daily, weekly, or as needed to retain moisture. The material should be damp, but not sopping or soaking wet. The gecko will most likely retreat to this hide when it begins to shed to loosen up the skin and help it come off easier.
Feeding ~
Leopard geckos are insectivorous, meaning they will only eat insects (live ones at that). Baby food including meat can be fed occasionally by placing a drop on the gecko’s nose, encouraging them to lick it up. Of course, this is optional. The best possible diet you can give your gecko is one with tons of variety.
Primary/Staple Insects:
Mealworms, crickets, and dubia roaches are all excellent staple feeder insects for leopard geckos of all sizes and ages. Superworms, locusts, and kingworms are great staple feeder insects for adult leopard geckos only due to their large size. Mealworms, superworms, and kingworms are all relatively high in fat, which makes them a great primary insect for underweight or juvenile leos and breeding females. Crickets, dubia roaches, and locusts are the healthiest primary insects.
Treat Insects:
“Treat” insects are those that should be fed to leopard geckos only about once a week. Butterworms, waxworms, and phoenixworms are good treats for leos of all ages and sizes. Butterworms and waxworms are very high in fat, so they’re fantastic for underweight, juvenile, and breeding female leos. Phoenixworms, also called calciworms, are exceptionally high in calcium, making them an amazing supplement to your gecko’s diet, reducing the MBD, or metabolic bone disease. Treats that are too large for juveniles but fine for adults are grasshoppers, woodlice, earthworms, silkworms, and hornworms.
Insects to Avoid:
Insects caught outside or in your home should never be fed to your gecko as they will likely contain traces of pesticides and/or carry parasites. Any insects that generate light, such as fireflies, are toxic to leopard geckos. NEVER feed your leo a prey item that is larger than the size of their head.
A Word on Feeder Mice:
Mice that are larger than the pinky stage and/or have fur on them are way too large for any leopard gecko and should NEVER be fed to them. Pinkies are commonly used for breeding females to help them gain weight. Pinkies are not as unhealthy for leopard geckos as fuzzies or larger sized mice, but are still not a good idea. They are vertebrates, meaning they have bones, unlike insects, which should be the entirety of the leopard gecko’s diet (besides maybe the rare drop of meat baby food). Mice are very difficult for leos to digest and are hard on their bodies. Waxworms, superworms, kingworms, butterworms, and mealworms either alone or in combination are great substitutes for pinkies as they are healthier for geckos and provide just as much fat content.
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Here's another caresheet, to get someone else's perspective:
http://www.reptilesmagazine.com/Care-Sheets/Lizards/Leopard-Gecko/
Most, if not all, of the information in the care sheet linked above is very accurate and trustworthy.