I did receive a response from The Needle Doctor, and it stated that the $50 is for an original Dual belt, which they purchase from Dual in Germany, and whose price has gone up with the devaluation of the dollar. They actually recommended the PRB belt instead, and said that when customers order the OEM belt, they suggest the PRB belt as a less expensive, but equally good, alternative.

Insofar as maintaining the belt, I can remember what AR suggested doing with theirs, all the way back to 1964: clean it with alcohol, and then dust it, not with baking soda, but with talcum powder. In all the years I owned an AR turntable, I never had to replace the belt.