"BillyBob" wrote in message

You're talking pennies if anything. Roller bearings can be had for under
$3
each in quantities of 6.

Not if you've already got the castors on hand. I usually keep a few sets of
cheap castors around in case of an immediate need or if I want to make
something mobile. The roller balls on the other hand while certainly being
nicely made pieces of machinery, are mostly dedicated to one use only.