Nicely done. It very much resembles a standard bicycle indoor trainer.
Sometimes you can find old ones (called fan trainers, as they used hockey table fans instead of magnets or fluid for resistance) for $20-50. They will generally fit a motorized bicycle with standard axle nuts (3/8 or 10mm axle). Some only seem to fit old road bikes (short axle length, about 125-130mm between the dropouts). The fan and flywheel part can be moved off the wheel or removed.
Originally Posted by 2door
Here's one, same idea, just steel pipe and some angle iron instead of PVC.
I like Dave's idea of mounting casters, maybe removable ones. This one slides easily on a concrete floor and it stays attached.
I've done engine tests on it so I know it's secure.