You've never heard of www.kbb.com or edmunds.com?
from a few hundred to a few thousand, have it checked out by a mechanic before you invest in anything though
It varies a lot and depends on the type & condition of the car, but here in the UK you could pick one up for a couple of hundred quid. You'd probably spend five times more than that on repairs.
I believe it would vary greatly depending on the car?