There is a very broad range here. Honestly there is no set value.
It can depend on a lot of things. First, what kind of computers are you aiming at? What game engine are you running on? Characters on high-end computers using the crysis game engine can handle 10,000 polys for characters whereas older computers running a basic engine use something more like 2,000-4,000.
But then again, that can change a lot depending on the game type. Will the characters be close to the camera a lot? If so you'll want more polys. If not, you want less so you can use more in other places and speed up the game.
Also, how many characters/objects/effects are on the screen at a time? That can change things a ton as well.
As you can already tell, it's all relative and there's no simple answer.