Prices for HP41 modules/peripherals

[DaveBr]

Greetings!
This is my first post. I was an HP employee from 1979 to 2013, joining HP right out of school. I have been an HP41 fan since I was issued an HP41C in December of 1980 - I still have that calculator and it works just fine.
I have been gathering up my calculator related items and I peeked at the prices on Ebay for some of the modules I have. I was absolutely floored at the prices! I assume the prices reflect the demand. I was curious, which module is the most sought after?

Dave