I'm pretty sure I can make my cleaner for less then one of those bar glass cleaners, especially after modifying it to work on beer bottles. Unless you can take a picture of a beer bottle actually fitting on one of those fat brushes I'll change my opinion.
I don't think the bar glass scrubber has a spinning center, like my cleaner will. I think the only thing it does is squirt liquid up into the glass as it is being pushed down... that motor is a sump pump motor which is meant to move liquid not rotate a machine.
The most difficult thing will be mounting the bearings and attaching the bottle brush to the shaft.
I'm now thinking that I should mount both bearings externally and then I only have to worry about a rubber seal with a o ring or maybe a rubber bushing, I would think I could cement the o ring or bushing right into the PVC cap(bottom).