Sheesh!
Yes, you CAN go cheaper, but you will likely have to give up some dearly held ideas about snake-keeping lol. If the hobby seems expensive, YOUR DOING SOMETHING WRONG.
Get the biggest tank you can afford off craigslist. People getting out of fish or reps will sell cheap - although they wont ask cheap. They will ask "a fair price, just what i got in it ...". Its YOUR money until you give it to them. INSIST ON A GOOD, LOW PRICE OR MOVE ON. Remember that the tank may leak, or may be cracked in a place not readily noticed, and if so, your buyer will NOT REPAIR. I am LOADED with free tanks that folks gave me. If I was inclined to buy a tank, I would not pay more than 30% of retail. Local TV station websites will also have a classified section, and this is a suprisingly good source for me to pickup unwanted snakes, which often come with enclosures.
Frozen mice are available at Rodents.com, and MANY MANY other places on the web. But you can also set up your own small mouse operation, and freeze them yourself when they reach the sizes you want.
Waterbowls? WALMART, 2 bucks. GOODWILL 50 cents. Heavy, large, flat-bottomed ceramic. Like a cheap CHEAP dog bowl.
Say whu? MOSS? I use sand YES SAND!! as a substrate. NO, contrary to what the uninformed posters will tell you, sand will NOT harm your snake. No, they will NOT ingest sand to form a digestive tract obstruction. BE A RESPONSIBLE KEEPER AND THINK ABOUT IT: when they eat in the wild, what are they eating off? Fine China? Paper plates? They naturally eat off dirt and sand, which they naturally expel to the extent ingested. If such was NOT the case, the snake would NEVER HAVE SURVIVED AS A SPECIES. Do NOT listen to these knee-jerk Know-Not posters. I've been doing this 20 years, and never had the impression that this was an expensive pursuit.
Here's more: I use hotrocks for heat. I have never seen a snake injured by a hotrock, probably because I bury my hotrocks IN SAND, which, as we all know, dissipates heat, giving the reptile a very convenient temperature gradient within which he/she can find a nice place to lay down. I submit that hotrocks are a good source of heat.
Here's more: I dont use hides. My snakes are there for ME to enjoy, and I enjoy SEEING them when I glance in the tank. I geatly enjoy HANDLING my snakes, and do so once a day, regardless of age. If I did not reap enjoyment by seeing and handling my guys and girls, I would simply let them go.
I use natrual appointments ONLY in the tank. No fiberglass or plastic garbage from PETCO. I strip the bark from fallen sticks, inspect for vermin, and wash in a 50-50 mix of white vinegar and hydrogen peroxide. Let dry before introducing to cage. Rinse if you wish. (This mixture BTW is an EXCELLENT disinfectant of bacteria, as good as anything on the market, without the perfumy smell. Use it to clean cages too. Also countertops, showers, toilet bowls, etc. Kills everything in its path.)
You can pickup suitably sized DECORATIVE rocks out of a creek, disinfect as above.
In a 40 gallon, a single hotrock may not be enough, and 2 hotrocks become cumbersome. Get an 8 inch metal round worklight - the silver kind - from harbour freight or lowes or home depot. My guess, 5 or 6 bucks. Purchase an infra-red bulb for it, and there's your heat source. For less than 15 bucks, your reptile has all the heat it needs. (Maybe too much, so buy a thermometer).
Skip the moss, the humidity spray whatever THAT is, the medicine spray 'cause your baby aint sick, and the shedding spray whatever THAT is. Keep a large, heavy, deep bowl of water in the cage, and with the heat lamp, the humidity will PROBABLY take care of itself. Buy a hygrometer just in case. Shedding is successfully accomplished in a relatively humid environment. Difficult sheds can be aided by misting WATER on the snake. Get a spray mister at the Dollar Store. For a dollar.
Skip all the "light bulbs." Dont buy em. But consider a UV light. Consider it, it may NOT be necessary.
I dont keep plants in my snake tanks. I tried it once when I first got snakes, and they just tore up the plants when they struck and the LIVE mice lol.
You can get your costs down very easily, and provide a more natural and pleasant environment for your snake at the same time.
Everything I have said here, everything you or the snake needs or wants, between 50 and 120 bucks, tops.