How much does saving in a 403(b) lower my take-home pay?

Less than you save, because contributions come out before federal income tax. In the 22% bracket, $300 a month into a 403(b) lowers take-home pay by about $234. Texas has no state income tax. Contributions still pay Social Security and Medicare tax, and withdrawals are taxed as income later. This is not tax advice: please consult your accountant.