What the numbers mean
A $75,000 salary in Seattle gives you $46,296 in purchasing power after state income taxes (0.0%) and local cost of living. The same salary in Denver gives you $56,457 — +22% more.
Median rent in Denver runs about $1,800/month — roughly $300/month less than Seattle's $2,100. That's $3,600/year back in your pocket before anything else.
Seattle's cost-of-living index is 162 (national average = 100). Denver's is 127.