Chassis dolly
If i can dig some pics and specs i did one once out of 3/16 4" square tubing and 1 3/4" x .120 DOM. Every 12" it had 2" long coupler nuts on the inside rail for 5/8" thread. Also had 6 legs with 1000lbs steel casters, and 5/8" threaded jacking legs. Later on i added removable 1/2" thick steel flat tops with 5/8" holes on 2" centers.
Back in 2017 I had about $550 - $700 in materials. Adding the table tops added substantial cost. Had 7 - 6' sections laser cut to the tune of around $1200.
Again this was over 7 years ago.