> ... [Dr. Decapitator] was willing to do it just for the cost of the donor cartridges and supplies. This worked out to $250 per coprocessor.
Sounds like there's some room for improvement in that market. Either that or Dr. Decapitator is one extremely generous dude.
There's some 3DS people trying to get a Chinese firm to do it, and they want $20,000 just to image the chip. No actual modification work.
You need access to machines and tools worth millions. Hobbyist level techniques like nitric acid and etchand sand to stain the ROMs just doesn't work even at SNES-era complexity.
It could be done for less in bulk, the issue is supply and demand. Very, very few people paying for this kind of work combined with wild costs for equipment.
http://byuu.org/articles/emulation/snes-coprocessors
It's a fascinating story.