When I first used ProStores many years ago they offered a free month trial and 30% off your subscription if you were an eBay store owner.  That has went away for the most part except for the free one month trial which you can find here:

One Month Free Trial! ProStores – an eBay Company

ProStores only offers a discount to eBay powersellers but it is still 30% making the Professional eCommerce Basic Plan $20.97 (Normally $29.95) and the Professional eCommerce Plus $41.95 (Normally $59.95).

Not sure if you want to subscribe to ProStores? Please visit the Squidoo lens “Is ProStores the right merchant solution for me?”