>>328965
Assuming you aren't in a no fun state, go ahead and get a cheap AR and upgrade it. I found some at a gun show in VA last weekend for about $560.
You could also get an AK variant, but that's up to you.
If shotguns aren't out of the question, look into the Remington 870. I have two and I love them. You can usually pick them up pretty relatively cheap, assuming you don't go for the camo'd out turkey hunting version.
If you buy anything that's got a detachable mag, you're probably going to want to buy more mags. You can't ever have too many mags.