At least a couple hundred. There are ways to save money on supplies, so I'll give you a few tips.
Tank: Craigslist is a great place to get cheap tanks. I got a 40g breeder for $35 just the other day. I would never buy a tank new with all the used ones that are out there for way less.
Lighting: You can use a regular household bulb as a basking bulb, and considering a 4 pk of bulbs is less than $2, you're talking less than 50 cents a bulb. You can get the fixture at Wal Mart or Lowes for less than $10 for a metal dome clamp light. Those work great.
A fluorescent fixture for your UVB can be found at Wal Mart for less than $10. They are the type meant to mount under cabinets, but you'll need to remove the plastic cover.
You can NOT cheap out on a UVB bulb! The Reptisun 10.0 fluorescent tube is really the only recommended brand of UVB right now. Any other could cause potential health and especially eye problems. You can get this bulb from somewhere like Pet Mountain or LLL Reptile for much less than in a pet store.
Thermometer: A digital therm is also a must. Again, Wal Mart has the Acurite Digital Indoor/Outdoor therm with a probe on a wire for $12. It takes the temp of the basking spot, the cool side and measures humidity.
Substrate: Sand is not only dangerous, it is expensive. Stick with paper towels (pennies), non-adhesive shelf liner (as low as $1 a roll at Dollar General type stores) or my favorite, tiles. Tiles are usually around $1 per sq ft, so you can floor your whole tank for around $5-10, depending on what size you have.
Decor: Fake plants, trees and rocks are cheaper at art supply stores than in pet stores. You can use river rocks or rocks out of your yard if you disinfect them properly by either soaking them in bleach or baking them. You can find cheap bowls to eat out of at dollar stores or thrift stores. A lot of times people will sell tank decor along with their tanks on Craigslist, so if you come across a cheap tank that is too small, but has lots of decor, buy it, and then re-sell the tank. Or when you do your tank shopping, try to find one that includes a hood and other tank stuff.
Even taking these thrifty hints, expect to spend at least $200 to get your dragon set up.
Don't buy the "kits". They often come with items that are potentially dangerous to your beardie (compact coil UVB, calcium sand, analog thermometers) so you would just have to replace half the stuff with the right stuff anyway.
Please continue your research at http://www.beardeddragon.org to learn everything you need to know about taking care of your dragon!
Best of luck!