Hi Guys,
After quite a bit of pain, we did eventually manage to build this natively using just the shopping cart (well 4 different carts to be exact) as per your recommendation Louie - thanks for the reminder on building the sheets outside the scene and also on the tip with imagemagik - that worked really well once we got all the scripts to work.
It was a long slow process getting all of the logic rules in place but we got a workable result in the end.
I think a custom IA probably would have been quicker and (as you mentioned Seb) the tradeoff here has been having to design a fixed number of lines in certain parts of the generated quote.
Thanks again for your assistance.