I think you may be shocked at the price, if you get a low quote I bet they will not be doing the job properly, anyone can slap a few floor panels and walls around and make it look good.
A and J were very good and explained how much work was involved to me - eg the ceiling joists are not floor joists and will probably need reinforcing, if you remove any props (eg from under-purlins) then additional reinforcement has to be put in place.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates