Quad bike tracking

I am looking for a few ideas on the below:

I am looking for a tracking system for quad bikes. The system must keep track of the bike over a 50km radius. The bikes can do up to 100km/h and I'm looking for updates every 30 secs. From looking around I thougt the best route would be to use a gpm/gsm device to a central console. From the console I can track bikes that get losts, or stop etc.

Has anyone looked at something like this before? Would it be more viable to build the circuit from scratch, or buy a ready make device - any device recommendations?

Any advice would be appreciated.

Thanks
Greg

Hi

is the place, where the quads will be (are?) used covered with GSM network?
What is terrain profile - can it be covered with VHF/UHF radio transmitter?

Are in the country VHF/UHF channels available to rent/lease?

Aprs

Do a little research on APRS. Amateur radio operators use this with transceivers and GPS devices to query and report on positions - often displayed on base station PC w/map overlay.

Yes - the tracks used are all covered by gsm.

I'll look into the APRS - thanks.