Now, now. thejellydude doesn't know that they'll be using his carts to rip off the game companies. He's only installing homebrew on them. I'm sure he makes them all sign a disclosure saying that the carts are only for homebrew and backups, and that he isn't responsible for any other use of them. Mmmm hmmm....
@thejellydude: how much time does it take you to order everything, download the homebrew and firmware, and put everything on the carts, and how much time do you spend helping everyone when a game doesn't work right or when they want to update their firmware, etc.? How much risk is involved with purchasing the hardware with your own money? Your cost should be around $40 - $45 each all said and done, so figure out how much your time and risk are worth on top of that and add it in. I agree, $90 (which is double your cost) is probably a bit high, but perhaps somewhere between $45 and $90 would be fair.
-Bri