Re: "...GPS blockers as notoriously used by so many professional drivers..."
"It could be self-funding"
_Use_ of a GPS blocker (or any other kind of jammer) in the UK has penalties of unlimited fines and up to 2 years keeping Norman Stanley Fletcher company.(*)
Selling them only has a £5000 fine and 6 months attached to it.
So yes, it could be a nice little earner, but I suspect the hard part would be getting the police to take any interest whatsoever in it. Perhaps someone at El Reg could get canonical statements from Ofcom and the Plod about how to report such things when they're found on Britain's highways and byways.
(*) I'll bet that using one in such a way that it endangers aircraft or railway systems comes with a set of even longer penalties. The ones above are just for the operation of the transmitter.