First clarification, this is just a boat that looks like a car, not an actual amphibious vehicle.

Second, as far as I can tell, JETCAR is a rental company and might not actually sell their boats. I'm guessing they're just a rental company and don't make their own boats.

https://watersportcar.com/ has models starting at $59k up to $109k

Around the turn of the century I used to go to a pub quiz at a place on the edge of a lake. There was a guy who used to drive there in his boat that had a body kit making it look like a BMW z3. He'd pull up, get out, lose the quiz badly every week and weave his way back across the water while completely drunk. It looked good at night because of the legit headlights on the water.