Saiga 7.62x39mm Rifle $300 (AK47 w/o pistol grip)
Based on the AK-47 design, produced on the same Russian assembly line.
These are popular military calibers -- that means cheaper ammo.
These do not have the pistol grip, but you can do a conversion and put one on for $100 or so.
Saiga 12 shotguns are $499.