Nothing wrong with applying a little bit of logic in deciding where you want to go. I think many of the people who are assigned to the LA County or NYC Health Departments are in for a rude financial awakening if they dont already live there. GS-5 is decent pay for many locations in the US but not for LA or NYC.
LA locality pay: $34,881
5% TSP contribution: $1744
PPO health insurance: $2210
This leaves about $30,927 to be taxed. Assuming that net pay will be about 65% of gross, the after tax income would be $20,103. Which breaks down to $774 per pay period.
I currently live in Koreatown neighborhood of Los Angeles, which isnt exactly posh, and the rent on my 2 bedroom is $1435 and probably going up 4% in August. This is cheap rent by LA standards. So if I stayed here and got a roommate, that would leave me with about $750 to cover everything else. Sounds like a lot, but it really isnt. Especially if you have a student loan payment, which Im assuming most of us do. Just something to think about for those considering the more expensive locations; the annual pay for NYC is only $500 more than LA.