I've seen them for servicing automotive build carriers that are easily good for 5k apiece. But you probably have to move them around with a forklift.
I did see a version on a construction site (think industrial, factory skilled trades construction site) that were something like 3" square tube uprights and something around a W6 wide flange I-beam section for the top, the bottoms were inverted C-channel. Single upright each side, no angled legs. More like a design of a hitching rail to tie up your horse outside the canteen

No need for X-bracing due to the heavy wall tube fully welded. Someday will attempt to copy but these aren't portable and likely wouldn't sit flat in many places other than a smooth-finished concrete floor.
I made some in my 20s which are 2x6s but use cross-tapped round-stock that screw together with socket head cap screws. Strong but not very portable and don't stack so well.
The folding plastic ones are my favorites, they are very strong and stack flat.