The soft core approach has many advantages, but FPGA companies have dropped the ball on single-unit (hobbyist) sales.

Chips that cost $1000 from a distributor cost 1/10th to 1/100th the price when you have a relationship with the manufacturer, mostly because distributors can't sell them very quickly and have to keep a ton of stock to have the SKUs you want.

On a modern FPGA, processor clocks of 200-300 MHz are possible to get with designs that aren't huge.

http://www.myirtech.com/list.asp?id=630 looks nice for something under 300$ AND 4GB RAM, but i think the embedded quad-core ARM is still faster than anything you can 'emulate' on the FPGA.

The Apollo project here would be particularly suitable as they have already iterated on the design using FPGAs. The chip is already working as an FPGA and bringing tangible improvements: I'm assuming a 130nm ASIC version would be even better.

I'm not sure that assumption is necessarily right. As a general guide, on a cheap (sub $200) modern FPGA I can clock an RV64 core at 50-100 MHz. As you spend more on the FPGA, you can get higher clock rates and/or more cores. Also it should be possible to clock 32 bit cores higher (perhaps much higher) because there will be fewer data paths for internal routing to skew. On the other hand, modern RISC architectures are designed for this, whereas old 68k architectures may not be.

I had no problem running PicoRV32 at 50mhz (maybe higher... 75mhz? can't recall, at that point I had other issues that might not have been CPU related) on an Artix 7 35t.

Honestly instead of chasing after new 68k silicon it'd be better to just emulate on a modern processor. Not the same romance, I know....but