robust + reliable != cheap and != Made in china
you need a realtime device (GPRS based tracking) .. or something just submit the position by SMS ?
if just SMS there are quite alot of devices out there can do this for arround 100USD already.
if the device also needed to work as "realtime unit" using GPRS .. its a whole different story .. and if you want your customers are happy and not flooding your phone with angry calls .... you should get quality hardware (which i haven't seen yet for less than 170USD)
Backups are for WIMPS!
(website position GpsGate Powered)