I think if there is sufficient interest you could get a group buy and costs would go down a lot, it's as easy to powder coat a dozen as it is 50 or 100. I know bulk prices go down the more you buy. Its laminated MDF balanced board BTW whatever forum legend says! Mana used a form of chipboard before MDF.
I would also investigate workshops in china as steel welding, powder coating and cost of palletising from one point may be cheaper than UK fabrication especially if you import at the material cost of steel... but they need close scrutiny on the material, bright common L section, not round or bullnose equal section. The welds ought to be line not spot, MIG not TIG, and check for blobby over fluxing ground back as they crack over time and are not as visually neat. All holes to be bench drilled and machine threaded to M8 not hand threaded with a hand drill as they must be vertical.
None of this is hard work or engineering beyond say an agricultural welding shop or garage.