You buy them by the piece. In the photo of ours the green are uprights, orange are beams, under the plywood is wire decking.
In Atlanta, uprights like this will run around $100 each. Beams like these are ~$22 each. Wire decking varies but usually between $8-18 each. Were into this setup about $550.
Our beams are 5" beams and 96" long.
The uprights are 6' deep and they were 12' high but I cut them down to fit inside. To get them already the right height was more money and I used the scrap to build a table base for the shop table.
These are not anchored but should be. With weight on them they're stable but they'd never fly like this in an OSHA shop lol.