Did you guys make an account with E-Bay?
I don't know the details, but there is some way you can sign up with them as an advertiser so that if anyone <a href>s from your site to theirs and buys then you'd get a commission.
If you do have one, then maybe a forum category for "I found this on E-Bay".
So that everyone that finds a motor, car, controller, etc... on ebay and decides to post it for others to see it may bring you in some commission to help keep the site going.
EBay's Affiliate program