This probably could have been in the Q&A.
Anyway, I'm not really sure. There are pieces of merch that were only handed out for specific events to a select few.
__________________
HAPPY HOL-ODD-DAYS!
I bought some powdered water, but didn't know what to add.
I think a better question would be "What is the priciest piece of Official Oddworld merchandise?", as then we would have an idea of the not only the rareness, but also the demand it is in.
But collectible items only have a specific monetary value when they're sold. None of the rare items are currently for sale, so we can't know how much they're worth.
__________________
:
Spending as long as I do here, it's easy to forget that Oddworld has actual fans.