Remember that patents don't last forever. If your friend really wants to cash in on this idea (instead of wasting money on the patent) he needs to start making them and making a profit, like yesterday!

Trust me, I've seen it a lot in the paintball industry. One company, Smart Parts, owns the patents/rights on most of the newer technologies within the sport, so no other companies make things like them. But, every year or so, Smart Parts loses a patent or two and the competition starts taking thier money/customers.