I've seen these being demonstrated on youtube. Was looking into them also at one point.
It would be simple to make your own - can buy castor wheels, plus more than enough metal tubing / wood, from hardware stores.
Plus ideally you'd want the Castors mounted on the outsides of the 'base' to keep its height low, so easy to push bike on and off without a difficult "ramp" to overcome.
Also!... you'd want castors with brakes, so the unit doesn't roll off while you are attempting to push the motorcycle onto it!
It might not even need to be full length (to accommodate all of the bike - both wheels). Could be just a foot long, for one wheel of the motorcycle, so the bike is pivoted with one wheel on the ground, to be able to rotate the whole bike 360 degrees in its spot and change its orientation. For example ride into garage forward - spin it around on the dolly 180 degrees, and its ready to ride out forward next outing.
No 10 point turn necessary (unless you have the luxury of a double garage)!