Depends on what's wrong with it. Could just need a new battery. Here is Apple's repair pricing. Keep in mind that Apple doesn't actually repair iPods, but replaces them with refurbished units of the same capacity and generation.
http://www.apple.com/support/ipod/service/prices/
There are many third party service centers that will charge less to actually repair whatever it is that is no longer working on the iPod.
B-rock