Just adding my two penny-worth to the debate re the last post:
It may well be as much effort to produce aircraft plans. But the cost of this time is presumably similar. The market for model aircraft plans is undoubtedly much larger, so the producers will sell far more copies, and can therefore sell them at a much lower cost per set to re-coup the same initial cost for the time spent.
I can say that the National Maritime Museum in Greenwich sells copies of its original ship plans, and these are about £50 - £60 per sheet for the basic draught, plus any deck plans etc for a bit less, as the sheets are smaller. It is quite possible to see these before purchase, although much smaller than the full size, which is 1:48 scale. These are colour scans, and show all the different coloured inks used in the original draught.
They do have all the 'Swan' class vessels mentioned above, including 'Fly', which has a beautiful 'as-built' draught, a work of art in its own right.
The 'Swan' class books by David Antscherl are extremely thorough and guide any potential modeller through every single stage of the work. They are well-written, and detailed in their information, with clear, neatly drawn illustrations. Even if not building a vessel from this particular class, they are very useful as an aid to understanding construction at this period.
I have no doubt that no-one on this site with any experience of modelling would have anything other than praise for them.
So if you are serious about building a model of 'Fly', and do not have much experience as yet, I would advise getting hold of a copy of the rigging volume, perhaps through a library or modelling club, to understand the quality of the product. The plans available are a complement to the books.
All the best,