I work with Garmin GPS antennas (more then I like to,) and I know they have several models that put out RS-232. I use the GPS 17HVS a lot. Most RS-232 antennas that I have seen require 12VDC power.
Depending out what your application is, you might be able to get away with a hand held GPS that has an RS-232 output. That way you could power it off of AA batterys.
Edit: Example
eTrex can be had for about $100. Just add Garmin P/N 010-10206-00 for a serial port or P/N 010-10268-00 for serial port, and cigarette lighter plug.