How much is a ipod 8 gig worth?

A minimum of $50, if its in good condition. Somewhere a little over a hundred will be about the maximum you could get unless you get lucky.

But it also depends on the generation of it, and if it isn't in good conditoin (e.g. cracked screen), and what model it is (Touch, Nano, Shuffle).

Touches are worth the most, Nanos in the middle, and Shuffles you won't get nire than $10-$25 out of.