The interesting thing about it is that it's the sum of it's parts. A dune buggy is cheapish (say $5k for a used one). A powered parachute is cheapish (say another $5k for a beat up used one). Extra parts and labor to put them together and we wind up at your brother's $12k figure. But can your brother's ghetto rigged dune buggy/powered parachute do 0-60 in 4 seconds? Can it hit 115mph? Does it have any range to it now that you've taxed both engines to their limit? Does it meet FAA regs?
Sure, it can be done for cheaper, but can it be done as well? As for the tires? Come on dude, it's a frickin promo. I'm sure for $120k they'll put whatever tires you want on it.
I don't think any of the para-gliders come under FAA regulation as far as design goes although once you go beyond the single seat very light ones you will need a "Sport Pilot certificate" from the FAA, here are the specs,
"Relative to a 2-seat trainer: Yes, you will need a Sport Pilot certificate. Your drivers will serve as your medical, and any restrictions placed on that will apply to your sport pilot privileges. This is an FAA pilot certificate. The minimum requirements are;
· 12 hours total time, with 10 hours dual training, that means you and your CFI in the plane together, learning to fly the powered parachute.
· 2 hours solo flight training. (yes, youre all alone up there when solo). 20 takeoffs & landings to a full stop, with 10 of those being solo.
· A dual cross country training with a flight greater than 15 nautical miles straight line distance between takeoff & landing point.
· A solo cross country flight of a straight line distance of at least 10 nautical miles between takeoff & landing points."
While the dune-buggy/flyer is cool @120K it's rather pricy, you can get a tricycle-style setup for around $15K and just skip the dune buggy altogether (or just buy a dune buggy stand-alone for a lot less than $120K) and enjoy both, just not at the same time.