For some reason not made known to me, the price of the Aurora bearings at Northeast Industrial Automation almost doubled over a couple of years when I was making kits - and I was buying full boxes of 20 at a whack. I just saw the MM-5 at about $15 bucks (single) on Amazon and back down under $10 on Aircraft Spruce:
https://www.aircraftspruce.com....php?clickkey=179496
I'm kind-of surprised at the price spread but I trust Aircraft Spruce for quality stuff and bought from them in the past, too, in quantity and was more than satisfied with their quality - WAY better than getting something from ACE Hardware!