no ideas on cost you would have to speak to your local welders as it would be a one off cradle built for your hull shape maybe ,Cookee or Adam Younger
who are both in the racing game could point you in the right direction, both are on ribnet and would more than likely have a better idea of who could make or even supply such a cradle, sorry not much use to you.
regards tim ps what about john at
www.quinquari.co.uk they build fit out large ribs maybe they would have some ideas
www.griffmarineservices.co.uk