I sold one once on ebay (pulled from a Tool), it sold for the starting price of 15€, only one auction from a member of the forum, and I had listed the auction in the ebay thread at the time...sorry it doesn't help you much!
While they were on blowout sale for next to nothing, the situation stands that they're one of the most sought after options for a TOOL... I obtained a used one in trade for a PS1 PSYQ cartdev. Now value on PS2 TOOLS has been rock bottom practically in the last few years, so that definitely affects the value. That being said, your PMs are full, and I'd like to send you a message!