I have been working on an online GPS tracking system for about 4 years now. The tracker we use the most is from Enfora. For about $130.00 dollars you can get their newest model with built in antennas and a 3 axis G sensor. It has a latching output to control a disable relay, a couple extra I/O (digital in, digital out and analog in). It supports different types of geofence and an overspeed. You should be able to find a service that supports this tracker for 10 to 25 dollar a month or you could roll your own if so inclined. Typical data usage is about 1 meg a month. I would shamelessly plug my service but I only operate in Brasil in partnership with risk management and insurance companies.