Just thought I would throw out this FYI- I was pricing casters for my new brutus system and came across this site. Super prices and quick shipping. They can wholesale their products as they make them in house.
I also used McMaster for the caster inserts (cost more then the freakin caster themselves!) but anyway what a cool company. I live in WI and since they are in ILL, I ordered Monday and have them already today! Wow
Try Harbor Freight I just picked up 4x 4" threaded casters for around $14 added another $2 for some 1/2" nuts to weld into the bottom of my frame and was done for less then the price of one from Homer or lowville.