whatever you buy, get something of decent quality. If you go for cheap chinese stuff, you will regret it later. Those crappy ones are cast iron and generally droung only on the bottom, on the slides and the jaws, and the ground planes are not parallel/perpendicular to each other. They also have a fair amount of play on the slides which causes the moving jaw to go up when you tighten the vise.
I guess cheapest you can pay for a decent quality would be around $100-120.