One of VERY many ideas:
Vehicle Tracking 100% Free for everyone
You buy a cheap prepaid phone (like Boost, Cricket, etc.) with a cheap data plan. Leave the phone on at all times in the vehicle (hard wired into the car is perfect)
Register the phone above, and then you can track it at all times. There are MANY variations out there. The cheapest being a cheap cellphone. Others have modules that you stick a sim card into, and you have to communicate with them via txt message. replies in text with coordinates, in which you have to manually plug into google earth or live maps.