Define "Regional Pay Differential"..

This should help you decide if their regional increase is fair or not.

http://cgi.money.cnn.com/tools/costofliving/costofliving.html?step=form&x=28&y=9

My Buffalo to San Francisco example…

Salary in Buffalo NY:
$60,000
Comparable salary in San Francisco CA:
$97,046.98

If you move from Buffalo NY to San Francisco CA…

Groceries will cost: 29.128% more
Housing will cost: 211.573% more
Utilities will cost: 37.254% less
Transportation will cost: 9.952% more
Healthcare will cost: 33.411% more

So that 15k raise they gave him was basically a big pay cut.