If in the South East you might try Parker Steel for the steel rod. Quick look at 12mm 230M07 and they are about 20% the cost of M-Machine but that is for full 3m+ lengths.
However you do really need to order in “bulk” as their own transport cost on top will make that expensive if you only buy one or two lengths. You will also need to be able to get a big lorry to your property and be there to unload the bundle.