You can get a brand new Ruger 10/22 (autoloader) for $200 or less at WalMart. Big 5 and other discount houses have them for about $210. If you want a sturdy, long lasting autoloader, they are about the best thing going. Lots of folks are drawn to them because of the large amount of aftermarket stuff available for that particular model.
Bear in mind the Ruger 10/22 comes in different "grades." That price is the birchwood stock, with barrel band, etc. For $300 you can have one in a nice walnut stock, checkering on the grip and forearm, etc. Or you can go the synthetic stock route if you think you want to get into the aftermarket "ultimate 10/22" game.
The triggers on the Ruger are terrible (very heavy pull). There are things you can do to lighten them up a bit, if you are comfortable taking a stone or file to the action yourself. Otherwise, you can hire that out or pay up to $280 to buy a very nice replacement trigger that slips right in and gives you a smooth adjustable trigger.
Another autoloader is the Marlin model 60 -- these can be found used in that $100 price range. Nice gun, but I sold mine off to buy the Ruger 10/22.
If you want a lever action, take a look at the Marlin 39.
If you want a bolt-action rifle, check out both Savage and the CZ line. Might be hard to find used, but the CZ model 452 series looks like a lot of value for the money.