Your math is worth little unless you plug the right values into the equation. He said his salary would be twice as high in SF, so for a 100k salary in Houston,

Your math is worth little unless you plug the right values into the equation. He said his salary would be twice as high in SF, so for a 100k salary in Houston, we're talking about 200k - 41k vs 100k - 17k, which is roughly a 70k difference (actually closer to 80k, but I wanted to make a conservative guess).