I'm not going to address whether paying workers less for the same job when they live in different areas is appropriate, but if you are willing to go along with

I'm not going to address whether paying workers less for the same job when they live in different areas is appropriate, but if you are willing to go along with the premise that it is than the reduction from 200k to 150k isn't out of the question for the areas involved. You didn't give exact areas but I put San Francisco and Denver into 5 different online cost of living calculators. Denver tended to be the most expensive area in CO these calculators had data for. They didn't agree to the dollar but in general the cost of living in Denver was reported as about 38% less with an equivalent living standard salary being $124,000.