
It's an expensive game to play. I'm surprised that some of the kit out there is as cheap as it is given the low volume runs. 2 years ago I had a bunch of boards made and stuffed based on a design using an 8051 deritive that ended up costing 400 dollars a piece, took 6 months to develop and it wasn't anywhere near as complicated as an accel. 90% of the work I did was pure software.
Yes, I'm familiar with how expensive even simple things can get. An 8051 would be relatively simple, since you might not need to involve surface mounted components and could probably get buy with a board based on a single layer double sided copper clad (and etched) epoxy board.
I spent a few months working on a Freescale MPC8641D based motherboard, only to find that the level of complication and the number of layers required (not to mention the expense) made the prospect of financing a production run almost impossible.
Considering that there are new '60 accelerators available, its probably reasonable to state that the demand for an '060/PPC accelerator would likely be limited. If you want to use a PPC, a SAM440 or a Mac (depending on what OS you wanted to use) would be more practical.
I was just thinking of my own interests, but you're right, the idea is impractical.