Just kegged 10 gallons yesterday in a ten gallon cornie. Drained the conical into it quietly, added diluted sugar, gave it some CO2 to seat the lid and burped it a couple times to get any air out. In a week I will attach my spunding valve the check the pressure and release some if it's too high. In two weeks it should be ready without refrigeration or using up my CO2. Maybe it's just me but the carbonation seems better this way.
In the past I have found ways to quickly carb but it rarely seemed to work as well as priming or set it and forget it. I must say that the quick carb does look like a cool brew toy though.
Here is my thought on building one. Already have a pump as a lot of us do that could be used for another task. Some kind of pipe, stainless would be nice, to make into a T, a carbonation stone, a fish tank aerator might even work, tubing and fittings for all if this. I'd bet if you scrounged around you could put one together for under $50 if you have the pump.