The cost an apple replacement varies by region (below I have put UK and UK links). If you do a bit of research, you will probably find a decent local company to do it much cheaper than apple. Finally, if you feel comfortable replacing the battery yourself, that would be by far the cheapest option (see here:
http://www.ifixit.com/Guide/iPod+Touch+4th+Generation+Battery+Replacement/9829/1).
support.apple.com/kb/index?page=servicefaq&geo=United_Kingdom&product=ipod&select=REPAIR_PRICING
www.apple.com/support/ipod/service/prices/[/QUOTEv]
Thanks. If it was not for the fact that I screwed up my iPhone 3g while trying to change the home button, I would have done it myself. I managed to somehow cut a PCB track and that was the end of that iPhone.