10 is just the fastest. Because it is a meta-benchmark, this rating is not necessarily relative performance, it is based on the position in the ordering. The achieved average FPS is just a factor in that, used to make the distance bigger to indicate performance jumps.

Example, fictional values: The 8700K is the fastest, because it was most often seen as the benchmark leader. It gets a 10. The 8600K has almost the same FPS, but it was always a bit slower, it gets a 9.9. The i5-8500 comes next, but its average FPS scaled to the 0-10 scale is lower, it gets a 8.7. Then the i5-8400, always seen as slower than the 8500 in benchmarks, would at most be able to get a 8.6, no matter what the average FPS says (with enough benchmarks average FPS become an almost meaningless metric, it's the position in the benchmark that counts).

That's why it is not possible to calculate price/performance with this. I could only highlight good deals, processors that have a high position despite being cheaper than the processors below. Which is of course already baked into the logic of the recommender.

Thought a bit more about this. What I can do is filter out all processors/gpus that are slower than cheaper processors. Proof of concept implementation: https://www.pc-kombo.com/benchmark/games/cpu?optimize=true. Those are essentially the best price/performance choices, with some restrictions as explained in the other comment.