There are dozens of sites that will help you calculate PayPal and eBay fees.

My favorite is PPCalc -

PayPal Fee Calculator

eBay Fee Calculator

Half.com Fee Calculator

Amazon Fee Calculator

BidPay Fee Calculator

ePier Fee Calculator

Etsy Fee Calculator

Overstock Fee Calculator

Throughout 2009, my goal is to clear $100 a month from eBay sales.

I use the above calculators to determine the starting prices of my auctions.