The prices are all over the place depending on the options. You might be able to find a plane jane ar-15 for around $750, but most are going to run closer to $900. You'll probably want to mount a scope, so te best option would be an A3 upper (flat top) which usually ads about $50 to the cost of a rifle (if it comes with a removeable carrying handle). You'll want a free float tube which adds another $100, and you might end up changing out the trigger for another $150. With all of the options, you'll be looking at well over a thousand. For about $1100 Bushmaster and a few other manufacturers make a AR set up for varmint hunting, which might be the best bet if that's what you plan to use it for.