I would tend to buy the item on eBid, if the cost difference was only pennies or narrow. The eBid seller's cost could have been higher. Seller's need to price their items in such a manner as to not suffer a loss in revenue. If you price your item below your cost, just to stay competitive with a seller who obviously has more buying power; that is like paying your buyer to take possession of your goods. Why would anyone do such a thing?
Would be interesting to hear about the results of your test.
I can not say for sure, but it may be possible that the balanced revenue from both venues combined, may represent the actual needed profits to justify costs. As far as where, probably where ever it will sell profitably.