What the numbers mean
A $75,000 salary in New York City gives you the equivalent of $35,936 in purchasing power after accounting for state income taxes (10.4%) and the local cost of living. The same salary in Denver gives you $56,457 — a difference of +57%.
Median rent in Denver runs about $1,800/month — roughly $1,400/month less than New York City's $3,200. That's $16,800/year back in your pocket before you factor in anything else.
These numbers use a cost-of-living index where 100 = national average. New York City's index of 187 means it costs 187% of the national average to maintain the same lifestyle. Denver's is 127.