Some updates:
I have written code to flash a N64 Gameshark in case it's bricked or just for updating if it doesn't have a parallel port.
And I also have compiled a parts list for 10 Cart Readers(without battery addon) for ~$300 which brings the price per Cart Reader down to $30 thanks to falling prices, economy of scale and the Winter Sale on Aliexpress right now.
Perfect for a group buy, a retro community or a maker space. One of you needs a 3d printer and one a PIC programmer.