It's more than "some pvc fittings and a plastic box"-such as a motor, threaded shaft, felt contact areas, assembly, marketing, overhead, etc. etc. and etc. Disparage it if you will, but the price shouldn't be a criticism-especially looking at what else is available commercially at that price point.
Yeah, it's not for me (that's one slow-turning motor) but I appreciate the creator's ingenuity.