Tony - it may be worth seeing if you have another local steel yard near you. My local supplier charge £4.1 +VAT per meter for 50x50x3 (£147.60 for 30m) as a base price & charge less than that if you order a reasonable quantity. I also get them to cut some of it to size for me - depending on quantities, they charge 50p per cut or less...this means I can fit it in my car & pick it up myself removing the delivery charge as well as saving me time cutting stock to size.
Do you have the name of the stockist, thats a fairly good price :)
i always check metals4u.co.uk for steel and their about £60 + vat for 6m