I don't know why these pieces of kit need to be so expensive. You could knock up a cheap Radalt for a couple of hundred quid these days, if that.
I like the idea of re-radiating ones GPS position. If everyone did it, there would be no need for transponders or even radar. Could even use the Mobile phone cells to collect the data, with no additional infrastructure required. Send it off via Inmarsat and you have glodal coverage.