What about instituting a kind of seal of approval? The selected price experts could (either by request or by default) put a seal of approval on threads where they feel the prices aren't excessive. This would be less intrusive and likely to cause friction than challenging prices in someone's thread, but it might have a similar effect in that people would come to notice the absence of the seal.
This could be done by pinning the top 5 (top 3, or whatever) Got Toys threads on the board that are offering the best deals. It would be subjective and people shouldn't take offense to not having their thread pinned if they think they are offering a great deal. It's just a general incentive to make more people take some pride in offering good deals on LRG.
I would expect the Top Deals threads to rotate pretty frequently because anything offered at a great price around here probably doesn't stay available for too long.
If something like this was done, I think you would see more people dropping prices on existing Got Toys threads instead of sticking firm to ebay-like prices. It would be a lot of work for anyone responsible for trying to select the top deals though.