there are a number of messages in the archive about where to get an A frame built but none on costs.
How much are frames running at by the bespoke builders?
Something to fit a Humber made in twin 1.5" tube, extra wide?
Give Gary at Spartun Marine a ring, he has that fabrication shop across the way from him that does allsorts of A-frame and custom stainless work, he'll be able to give you a good idea of costs.
