When we did ours, I managed to find an old boy who was winding down, just doing one big job a year, working 6 months, then taking the winters off. As a result, he had de-registered for VAT!! Bingo, saved 20% right there!
Definitely get 3 when you come to actually making a decision on who to go forward with, but at this stage I think it's just a case of talking it through with someone and getting a feel for what the ballpark cost will be.
Don't base your thoughts and plans around the numbers we throw at it, because we simply do not know enough about the spec, and finishes you are after. get a couple of builders round to quote for an all-in price, and take it from there.
I think you'll find the route to paying for it is from...