Ebay: help me with the math
 

Looks to me by the time you sell an item, you pay about 15% in fees if it runs through paypal (on average)...sound about right?

eBay
 

Yes, here is the fee table, 15% is about right a bit higher on BINS under $20 or so.

http://pages.ebay.com/help/sell/fees.html

Fee Calculator
 

And here is an even more helpful fee calculator where you can plug in different #'s and it will crunch the numbers for you:

http://www.newlifeauctions.com/calc.html

After plugging in some #'s it looks like $500+ BINS would be more like 10% but under $100 items the fees start to jump up to 15-20%. I think if you get a store you could lower this but I've heard you need 200-300 items a month listed to make it worth it...Also you could auction at .01-.99 and save on some of these fees but then you are rolling the dice

I generally start auctions at $0.99 and end up paying 12-13% in fees.