Try the Yugoslavian SKS. The ammo costs about 10 cents a round and the rifle can be purchased in fair condition for 150$ from a dealer.
Be very wary of those ultracheap rifles from China and third world nations. Some are fine, but others are very dangerous . . .and there is no obvious way to tell the difference.
We have a case here in the SF Bay Area of a guy who was at an official range in the Santa Cruz Mountains, using all the proper safety procedures. But he had a cheap Chinese rifle with even cheaper metal components.
He squeezed off one round, and as he did, the shear pin (the tiny clip which holds back the additional rounds in the clip) snapped off -- instantly turning the rifle into an automatic weapon.
A fraction of a second later, just as he release his grip on the stock, the second round unexpectedly went off, recoiling the rifle backwards off the table and butt-end into a stack of sandbags five feet behind him.
The third round went off just as the rifle hit the sandbags . . .and out of bizarrely bad luck, the bullet hit the shooter right between the shoulder blades and killed him.
The odds were probably a million to one. But any time you've got a gun that can go crazy on you, you are putting your life at risk.
As an aside, a buddy of mine in Montana told me he had bought one of those Chinese guns at the local Wal-Mart or some such place. I told him that I prefer my friends to live as long as possible, and sent him $500 to buy a Remington.