I've been doing some more research on the coin, and one possibility that I think is worthy of discussion is doing a ceramic "poker chip" coin instead of a metal coin.
Advantages of this style of challenge coin:
* Less constraints on the artwork - finer printing, more colors. We could probably do a coin with "Rocker" Priss on one side, and the 4 Knight Sabers (or the Motoroid) on the other.
* Better economics (in particular, low setup costs), which means either we can get a bigger coin for the same money, or free up some budget for other things.