It depends on how much coffee you consume, because different models roast different amounts. A good starter unit is the Fresh Roast, which is both inexpensive and easy to use - the only drawback is the 3 oz roast load, which is enough to make about 12 cups of coffee. Still, it's a very fast roast, so you can make enough to last you the week fairly quickly. It's also very good for darker roasts. They're at
http://www.sweetmarias.com and sell for $70.50 without beans, or $80.50 with a 4 pounds of beans included.
If you drink a lot of coffee, you can occasionally find an Alpenroast on eBay - it's a small drum roaster that roasts 1/2 pound at a time, and it also does well with dark roasts. It'll cost you around $250, but the larger capacity might be worth the money.
I have an iRoast, which has a much larger capacity than the Fresh Roast - it does an even cup of green coffee per roast, and it's programmable, so I can customize the roast profile. You can find it at Sweet Marias, but
http://www.coffeebeancorral.com sells it for a little less ($170.00).
There are tons of very inexpensive ways to roast - a lot of people roast coffee on their gas barbeques, using a roasting chamber that fits onto the rotisserie (cheap, and does about a pound a pop). People modify popcorn poppers. Check out the forums at
http://www.coffeegeek.com (look under 'home roasting') if you want a little more information on some home-grown ideas to roast without buying a roasting appliance.
You can find beans very cheaply at
http://www.greencoffeeco-op.com I can find some excellent estate coffees there for under two dollars a pound (I think they have one up there now that sells for ninety cents a pound).