You might try using google imaging rather than the listings !! Take each artist and see what some are selling for !! Remember there were a lot of these done and finding an exact duplicate is not necessary for a value !! Just get in the ballpark with what each artist is selling for. Also think about this,, there is an asking price and a selling price,,not always do the twain meet !!
Forgot to say that ebay is pretty good to see what is moving and what type get few or no bids !! Just change the "Sort By' menu to "ending soonest" And look at the ending prices !!