In the space of possibilities this can be abstractly thought of as a Caravell [1] harness gone wild. But if you had to price access to the project in a commercial sense, then, the pricing is going to be quite high. Because it's not just the cost of the masks - there's a whole lot of talent and skill in the team that does the "backend" processing. That is, once the RTL is done, it goes through multiple passes of place/route/timing, ATPG, DRC, LVS...and that's just to get to the tape-out. After that there's still more to do with the chip probe, packaging and reeling.
The open-source argument is that if we could make that back-end part more transparent, then, we could improve the tooling and thus decrease the labor. But, even a single mistake at these backend steps can scuttle a whole mask set. The methodology is incredibly incremental, scripts are handed down for generations and there are magic settings in them that make things "just work" and nobody quite remembers why or how but it was probably a lesson learned the hard way so we just leave it that way. And it's not just the money - the iteration time through a fab is months. So you have to be a bit careful about prioritizing your experiments and your risk budget when trying to make progress in this field.
I am lucky in my case because what I want to do aligns with their original commercial interests, so the strategic benefit makes things worth the tactical risk. Frankly a big part of the project overall was just figuring out how to scope things so that we both came away reasonably satisfied in terms of risk and outcomes. Would I like things to be more open? yes. would I liked to have put an opentitan core in there? yes. Would I have been able to take advantage of more back-end support to do a faster CPU? yes. But, we had to constantly balance tactical risks, and even if I don't agree with all their decisions, I have to respect their experience.
[1] https://github.com/efabless/caravel
