Perhaps one of the absolute cheapest ball bearings assemblies is the
infamous skate bearing. They're cheap enough I buy them atleast a dozen at
a time for misc projects, and just have them on hand. I probably have 30 or
40 of them in my spare bearings right, not and a small package of them in
the center drawer of my desk. You can get them in better grades if you want
to, but the plane old cheap import version holds up just fine for hundreds
of projects, not the least of which is skate wheels. They are even cheaper
than buying bronze bushings from most of the common industrial suppliers. I
know. I have a few 8mm bore bronze bushings on hand too.

I've wondered about this for years. I think I might even have asked this
group before. Is there a big brother to this bearing? Something bigger and
nearly as common so that it can be priced to keep a bunch of them on hand
for miscellaneous project?