SKS. Prices are coming back down a bit. Not the best accuracy, but
they are reliable and ammo is available. And they are a heck of a lot of fun.
For not much more than the price of the SKS you can get a bottom end
AR. Recently saw some with a polymer lower for $399. Hang an inexpensive
optic on it and you are still under $500.
In a bolt action the Mosin Nagant is probably the most bang for your buck.
If you don't care if it is 100% original, there are LOTS of "sporterized"
1903's, Enfields, 1917's, etc. out there for not much money.
CMP Garand. A piece of history and one heck of a rifle. Get one while you can.