My guess after building it would be that it would come in around $100 to $150 depending on what you have around for 3D printing and so on. Unfortunately, I recall there being a bit of a jump in component prices circa 2020 that really hasn't resolved itself.
As one of the other commenters mentioned, keyboard switches don't come cheap. Your best bet would be to look at some of the sources for Cherry MX clones, though for my build I was able to find a US-based source for Cherry MX switches relatively cheaply. It also helps that you don't need nearly as many as for a full, traditional keyboard.
Another cost to consider is the cost of the PCBs. All of our boards (including the prototypes that didn't go anywhere) were done by Aisler and were a bit more expensive than Chinese board houses, but they always came through and I was too lazy to shop around. Per board the cost isn't bad, but consider that you're buying boards in groups of three, and then you have at least two PCBs (the main board and the keyboard).
It's also going to depend on where you live and what kind of import duties you might get hit with.
The two most expensive parts are probably the CPU ($14) and the Propeller 1 ($12). If you have a 3D printer, the entire project is probably well under $100.
> It shouldn't be too hard to replace the "custom" keyboard with a ps2 keyboard and do the ps2 driver on the propeller
You might be surprised at the knock-on effects of that.
You're not going to be able to drop in the PS/2 driver from the OBEX that easily. The Propeller has 8 cogs. Right now one manages the 6502 bus, one manages the SID emulation, one manages the NTSC video generation, four are in use for scanline rendering, and one is used to implement two separate UARTs via coroutines. So you have no free cogs, so unless you can wedge your own PS/2 driver into the UART or SID code somehow, you have nowhere for it to run.
Also, the Cody Computer has its own ROM in 65C02 assembly, and that has its own I/O routines written around the idea that it's scanning the keyboard using the 65C22 VIA. You could change some of the ROM so that it would read the PS/2 input from the Propeller (assuming you could solve the above problem), and most of the programs in Cody BASIC would work as long as you consistently translate the data. However, assembly language programs that directly scan the keyboard matrix would be completely incompatible.
The joystick ports are also scanned as part of the keyboard matrix, so you'd have to keep that separate, ditch the joysticks, or something else. That means that you don't really have the option of deleting that much code, which poses another problem because the Cody Computer's (emulated) 8-kilobyte ROM is already full from the BASIC interpreter, runtime routines, and default character set. You can also move that around and expand the boundary, but again, that introduces yet more changes so it would be harder for people to share programs, particularly low-level ones. It also reduces the sense of it really being a retro 8-bit computer.
If the Cherry MX switches are too expensive, you've got better options:
1. Buy some knockoff switches off Amazon, Alibaba, or whatever; I'm seeing 32-packs of Cherry clones for $10 to $15, tops.
2. Get a piece of junk mechanical keyboard that's really only good for scrap and try to desolder and salvage 32 of the switches.
3. Redesign the KiCad file for the keyboard to take tact switches. That said, if you're going to buy a board, an additional $10 or so for switches isn't that bad.
(The very first keyboard we did actually had more keys, but all of them were tact switches; it was a neat keyboard but it wasn't a joy to type on.)
