Yeah, parts for those 350's are hard to come by now, especially here in the UK!
Postage shouldn't cost to much, about 8 quid or thereabouts.
Manufacturing cost... I'd estimate £30 to £40, time and materials depending. They will come oiled (to prevent rust), not painted.
Also, these will be custom made and as close to OEM as possible, please don't expect an exact replica.