Send GPS coordinates via VHF
FOR LICENSED HAM RADIO AMATEURS ONLY!!
This is what Theran says:
APRS is the solution.
There are several sites to track your APRS position.

aprs.fi
openaprs.net
...

Frequencies can be found on the APRS wiki.
Low budged APRS transmitters
A Tinytrack is a Terminal Node Controller (TNC) you can couple to almost any modern VHF car transceiver.
Or a microtrack with buld in tinytrack 3 chip.
See the byonics web site.