I think everybody would feel sad if somebody has sold you a 18kg tube to put on top of your boat, when you discover that you could have bought a carbon tube for the same price: 500£ What is cost effective in that for the buyer?
The quotes I held at the time (even from Stealthmarine directly) were considerably higher then 500 pounds.
Wouter
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands