This is a zombie thread, so some of the information is ~2 years old. I recognize that the basic question ("What kind of .308 rifle can I get for <$500?") is still a valid question, but I'm going to ask that folks who still have questions about this start a new thread. Given the recent climate in firearms sales, I suspect lots of the old price information needs to be updated, anyway.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.