with eBay you pay:

eBay charges a monthly "store" fee for every store you have  ...  and ...  an "insertion" and  "final value" fee for every product you have.

So if you have ONLY one store (the least expensive) in which you sell ONLY 25 items a month for an average of ONLY $12.50 each 
TOTAL SALES = $312.50        "Insertion" fee = $13.75,  "Final Value" fee = $27.34,  monthly "Store" fee = $15.95
TOTAL fees = $57.04