CHIPnTRAC GPS tracker was recently featured in Modern MINI magazine (Sep-Oct 2012 page 64) it has a one off cost of £149 and is popular with classic car owners for diy installation. More details here: GPS Tracker
GPS Security Tracker: A self-monitoring unit which uses the GPS navigational system to determine its position and then communicates this information using text messaging to up to five authorised mobile phones. You can dial up the unit and it will reply with a text message giving its GPS co-ordinates; or you can set it to inform you if it moves outside a given geographical area. The only costs in addition to the purchase price will be the cost of a SIM card for the tracker and your network's charges for text messages.
When you park your vehicle, just text an instruction to Stockade and if the vehicle moves you will receive a text message on your phone. Thereafter you can check the vehicle's whereabouts by calling the tracker, which will reply by text message with its new co-ordinates. If your vehicle has been stolen, you can inform the police, give them the details and let them do the rest.