Bob Minchin (myfordman) AKA 9fingers made a cheap version of these retractable casters using 40, 50, and 60mm box iron.
He has plans for them if you look.
I used them for my bandsaw. one thing I noted with my thinner walled box iron was damage to my good boots when disengaging them, the second time round I made these, I made sure to weld a bit of metal on the end so they weren't so sharp, aswell as making a little more area of the flat foot lever on the underside, so it won't get stuck.
Kinda a faff for a workbench to go about each corner of the bench IMO
I made a thread and youtube titled 'a wheely good workbench solution'
Another good design might be another retractable caster design by a youtuber called riverbuilder.
Another fella worth looking at is Carl Holmgren, he has quite a few retractable caster designs, once you use a single lever design you won't go back.
I can't link anything as the internet is very bad at the moment.
Tom