Shuttle bus tracker

Not that I tend to err, leave things till last possible minute or anything, but I'd really like to have a tracking system on the CERN shuttle busses, so that I can stay in the office until I know the bus is coming. (or, armed with a mobile device waiting at the stop, see where it is)

So - I was thinking something embedded ish that contained a cheapo GPS chipset (probably good enough signal on the dasboard, a 2 line LCD and a keypad

something UI ish for driver along the lines of 'select route:'
and then it'd show the route, upcoming timetabled stops

backhaul to site would be GSM (should be able to transmit a small UDP packet of transponder#,Route#,Position,timestamp) to a central server.

The folks over at rpi.edu (yes, they started concerto too) already have some code that looks interesting at https://github.com/wtg/shuttle_tracking/


Question is, would it be cost effective to roll our own, and if not, who's offering the best / cheapest (open) system out there?