Again, cost is relative to hardware you have. If you own a supercomputer already and you want to run chess on it for whatever reason it matters what the performance you get from each algorithm on that hardware. If your going to buy new hardware it's design depends on performance across every algorithm you expect to use.

So, the only case where chess performance per $ matters is if you are only going to ever use that hardware to run chess. In every other case which is the vast majority of the time you care about diffent metrics.