I've got an idea about lots. Put a checkbox next to the purchase price field that says "lot purchase price" or something. Then make sure that any price entered as a lot purchase does not get figured into the current member pricing data.
So for example, let's say I go modify my Reflector entry in my collection, add a price of $9.99 and check the box. Give the user an option to link additional records to the lot. For me it would be Dead End (G1) and Cindersaur (G1).
Now say another user goes and looks up Reflector, below the User's value table, have an AJAX link that says "view lot pricing". Click on that and you can see the high, low and average lot price entered by users where that particular record has been tagged. That way a user can see the stand-alone value and lot value.
BUT, make sure not to tie those prices to people's collections. If you look at my recent additions, I did not add Cindersaur because it was a dupe (I don't add dupes into my collection here), so make sure to tie it to the figure record itself, rather than the figure record inside of someone's collection.
That's my grand idea.