With respect to casters -
Amazon has the POWERTEC 8 Inch Caster Wheels Set of 4 (2 Swivel & 2 Fixed), Large Rubber Castor Wheels (17055V) on Prime day sale for $70.
(spelling from website)
And with respect to putting heavy equipment on casters. I've got about 2,500 sq ft of good concrete floors in my she'd in Mississippi and a lot of heavy stuff. My solution early on was to buy Harbor Freight 18 in. x 12 in., 1000 lb. Capacity Hardwood Dollies. Back when I first started buying them the were like $6@. I use 3 for my 6 inch chipper, 3 for my 5' tiller. just have to push them around occasionally to avoid flat spots
I even have a couple of 8' tables resting on them so I can very easily reposition the tables.