Not sure about eBay module but the lowest CS-Cart price is offered by CS-Cart resellers. The lowest possible reseller price is $345, you will not find a cheaper CS-Cart by official distributors. You are welcome to check our offer http://www.alt-team.com/cs-cart-ultimate.html
If you have a small business, you may consider a free CS-Cart version, probably it will meet your requirements Prices - CS-Cart Multi-Vendor
Best regards, Alt-team
I can advise you to contact CS-Cart sales team directly at email@example.com to find out if any discounts can be provided to you.