Hi everyone... As my nickname would suggest, I am the guy who designed and developed this floppy emulator
Contrary to what one might imagine, the keyboard interface and video overlay circuitry are not expensive at all. The video overlay circuitry basically consists of a 74lv244 which costs about $0.5 (single) and the heart of the A500 keyboard daughterboard is a PIC24F04, which costs about $2.5 (single). The keyboard daughterboard is just a single-sided PCB, which also helps reduce costs.
The most expensive component on the main board is the PIC32MX575 microcontroller, which costs about $10 (single). As with most homebrew, low-volume projects, I would expect the PCB cost to be the highest value in the equation, but that also depends on the volume. There are a few hidden costs such as the wiring harnesses and cabling but I would not expect those to add a lot.
So, I guess, in the hands of the right people, this project could be manufactured and sold for a reasonable price. Unfortunately, I do not think I am the right person, because of two main reasons: First, I do not have enough time to devote to a commercialization effort (as this is mainly a hobby project for me), and second, I have no experience in that area.
Anyway, now that I am here, I would be glad to answer any questions any of you might have...
