Some of the better casters at Harbor Freight are not sold on the shelf with casters, but instead come as part of the four wheel moving dollies instead. It's actually often cheaper to buy the dollies, yank the wheels off and have a good set for little investment.
EXACTLY! Buy the small dollies for 8 bucks on sale...
Here are a few of the dollies I have "repurposed" ...
The welding/grinding/assembly bench I built out of a trash picked vanity
Cut down a full size dollie and bolted it under my tubing bender stand.
The engine for the van is sitting on a full size dollie. The cradle is screwed to it so it won't come apart.
The trans and GV unit are also sitting on one as is my arbor press.
I even used a small dollie under my roll-a-round work stool after the cheap casters blew out.
Mark