It would be cheap nowadays, the soc would be extremely tiny... however to get cost down, you would have to buy wafers in bulk, which is very expensive.

It would only be cheap iff you can find several million of people who are also willing to buy said device.

There are typically two ways to approach selling a chip, using ASIC(application specific integrated circuit), and using FPGA(field programable gate array)

ASIC has the advatage that if done in mass production, its per unit cost is very low. The requirement is that you have to make that order of mass production, which is only feasible if you have a target audience willing to buy it (e.g phone chips, new gaming consoles, gpus)

FPGA are essentially boards that can be programmed to act like a new chip. Their cost is high to start, but does not require the cost to mass produce it, making it cheaper than ASIC if you only need a small quantity.

For an economic purposes, its far cheaper just to use a modern cpu and emulate the hardware than it is to make a new line of such an old cpu. No additional hardware needed.