I can see someone paying 5$ to case a Pokemon,Zelda,Final Fantasy,Dragon Quest (top tier games)
For myself, a semi serious collector, the price would need to be much cheaper, near the 1-2$ area to consider it based on total cost.
I had my Game Boy collection on ebay near christmas and several Mint CiB games I had went for under 5$, with a few going for .99 cents.
I think the market for 5$ cases would be the top few % of game boy game collectors (who mainly go for boxed only), and general collectors for a select tier of games.
By lowering the price i think the Demand would be higher, and open the possibility of smaller game stores to order. I dont think there is a single store in my area with 1000 game boy games for sale to make it into the price needed to make it worthwhile for resale. I sincerely wish there was, I would be there today.
I do sincerely appreciate the effort and time you are putting into this. Its refreshing to see others so passionate about there hobby.