Cost of repair is going to depend on whether you have Apple do the repair or a third party service. Here is a list of Apple repair costs for the different generations and models of iPods.
Note that Apple doesn't actually fix the device, but instead does an out of warranty exchange for an iPod of the same model, capacity, and generation for a flat fee.
For third party service pricing, you'll need to do some of your own research. Just Google "iPod repair" and you should get back a plethora of results to work through. From there you can decide whether to go the repair or replacement route.