in the end, you're basically throwing away a tablet, GPS receiver, cell phone, and solar panel, right?

OH, hey, don't they have standalone GPS tracking devices with some kind of base station to monitor their location? then you wouldn't have to worry about the cell phone component, and you could just give ME your n800.

EDIT:
here you go. £150, though. hmm....
http://www.snooperuk.com/products/snooper_tracker/