I saw the flatpacks too, pretty expensive c.f. the s1 club ones when you factored in paying someone to weld it all up. iirc the flatpack was c£1500 and the s1 club c£1800 bit of a saving if your welding was up to snuff though.
I should imagine welding a flat pack to be spot on is considerably more difficult than patching a holey chassis.
is yours not patchable @sidog11
I think you are somewhat out on the cost of a club chassis ( if they were available) . A price of £2,500-3,000 would be nearer the mark . You can barely get a new bulkhead for £1,800 .