I had my boy Winston neutered at a clinic linked to our local humane society. They were great and the rates were very affordable (neuters/spays not over $40 with a microchip option at only $25.)
Most of the programs out there are really affordable, and in my experience a huge portion of the staff is going to be there because they love animals.
I believe there are quite a few options in the brooklyn area, including this one that seems really interesting.
Spay/Neuter Certificates
Depending on your income level there may also be programs that will spay your girl on a sliding scale (which can mean little to no cost for you.) I know the ASPCA has a program near you as well as BARC (
BARC :: Brooklyn Animal Resource Coalition :: 718-486-7489). I would think they might also know about some other programs they could recommend as well.