That's an interesting take that I didn't consider - that console manufacturer can charge money for the guarantee that the games will work.
However, from a quick google, two sites [0][1] have tried to build a PC with the same specs as the PS4 Pro ($400) and came up to ~700.
[0]: https://www.gamespot.com/articles/we-built-a-pc-using-ps4-pr...
[1]: https://modcrash.com/the-ps4-equivalent-pc-build/