If it cost you £300 just to blast and galv, the £850 I paid and the £775 @mgd109 has been quoted seems incredibly reasonable considering that includes and acid dip to strip it, and all of the parts and labour for the repair work required!I rebuilt a second hand bulkhead then had it shot blasted and galvanised cost me close to £300 to have it blasted and galvanised.
Plus the many hours to make it good that was in 2010 no issues yet. Other than paint lifting off galvanising as I did not T wash it just etch prime.