You can by some parts over ebay, but you must buy the receiver assembly from a gun dealer. Most peope just go down to Walmart and buy a 10/22 for $150 bucks, then they go to ebay or a gun show and buy all that other crap. Myself, I'd just save my money and get a Mini-14. In the end it will be a several hundred more invested but you will have a serious weapon instead of some wannabe assault rifle. Another good choice is to customize an M1 Carbine, but they are no longer as cheap as they once were. You used to be able to pick up an M1 with a junky stock for $200 bucks at a gun show, and then get a folding stock for about $100, and you could pick up any kind of military stuff like banana clips and flash hiders at the gun and militaria shows. I think most of those prices are current, but now the junky M1 costs $400. Otherwise, save up a grand and get an AKM or an AR-15. Personally, if you want a folding stock weapon that is reliable and bad to the bone and not too overally priced, an AKM is hard to beat. Stick this one in your sock:

http://www.gunsamerica.com/guns/976497575.htm