I have a couple of GPS trackers one of which is mounted in Time Bandit. The other I have sitting around, it is from eBay
and is actually a chinese copy of the one I have in the boat (also chinese) the reason I bought the original was becuase I was getting some false alarms from the copy when I set up the "Move" option which basically texts you when the boat moves 200metres from its set location. However I have since found that this was actualy due to where I had it mounted as it was getting interfernce from the metal casing of the VHF.
If you want my spare you can have it for £25, you will need to fit a pay as you go Simcard in then follow the instructions. It has a battery life of about 36 hours I have 1 battery as I am using the other one in mine however you can buy a 12volt converter from ebay here
which powers the unit from the boat battery this was about £10 it is small enough to fit under the cowl of an outboard or anywhere on the boat. (smaller than a packet of fags).
Let me know if you want to give it a whirl.