Umm... well, M-14 clones or M1A's aren't cheap.
Best thing to do, is to go to
http://www.m-14forum.com and browse the classifieds for a Poly-tech M-14. Cheapest you'll find an M-14. M-14 style rifle comes in .308, you know that right? Is that what you want?
For $300 - $500, look at the Mini-14, it mimics the M-14 (kinda) and shoots the .223 cartridge, which is less expensive to shoot.
Are you going to hunt? You've mentioned that you want to hunt deer, then switch barrels for bird hunting. Right now, I'll tell you that there is no place for a bipod on a hunting rifle, NOR a shotgun!
If you're gonna do some target shooting, well the M-14 is a great autoloading rifle, its accurate to boot, but it ain't gonna be had for $500. Cheapest I saw was a Poly-tech Chinese M14 for $800.
So answer a few questions for us ok?
What are you shooting at?
Why a bipod?
Does it have to be a semi-auto?
If you're hunting deer, would you not like a bolt action rifle?
Do you want a shotgun or rifle, first you mentioned shooting deer, then bird, now it seems you want to shoot targets?
What caliber/gauge?
Tell us a little about your firearms history.