Are these something that might be considered on bidding pond or anywhere else?
Post a desired good or service and the amount willing to pay for it, sellers can bid you down if they wish to undercut one another.
Since biddingpond is not financed by commission it doesn't seem like it would hurt the revenue of the site in any way.
This idea was suggested and will eventually be implemented. Unfortunately I do not have a time table for this feature and someone might beat me to it.