You could easily sell 10,000 cases at $1-$2 a case, but at $3-$5, it would be much harder. If you want proof to this, most case reselers on eBay who sell $5 cases with art, have not gone over 2000 transactions.
I think it would be best to take less of a profit on each case, and require more cases sold to recoup losses. You would sell more at a lower price, so it should even out. I would ditch 3DS for these at around $1 for bulk orders, I would need a case of 100. I'm sure you could sell a few 1000 to people on this site, with the conversion easy due to the size being the same as DS cases.
Do you have more images of the cases with different games in them? Does Robopon, Yoshi Topsy-Turvy or Pokemon manuals fit?