What the numbers mean
A $75,000 salary in Boston gives you $43,981 in purchasing power after state income taxes (5.0%) and local cost of living. The same salary in Austin gives you $61,983 — +41% more.
Median rent in Austin runs about $1,700/month — roughly $1,100/month less than Boston's $2,800. That's $13,200/year back in your pocket before anything else.
No state income tax in Austin. On a $75,000 salary, that's roughly $3,750/year you keep that you wouldn't in Boston.
Boston's cost-of-living index is 162 (national average = 100). Austin's is 121.