iirc, they are a few hundred bucks.

After seeing this a few months ago, I grabbed a sketch pad and doodled a design that would accomplish what that one does.

You could legit throw one together for about $30 using 2 mason jars (with lids), a tube of aquarium safe silicone to to build the inside chamber (no water or smoke touches this area). A length of brass pipe (available on Amazon), and a couple of brass fittings.

Won't give you exact plans as without seeing the guts of the one Seth used as it may be the same design.

When you rotate it, air should naturally suck in the intake and spit the last rotations air out of the exhaust. If you can figure out how to rotate it and cause an air only output, you can build it super easy. Cleaning would be as simple as unscrewing the jars, clean em, and pipe clean the intake/exhaust.