First of all, you need to understand the difference in terms:
Shell builders, build the shell, hull but rareley fit-out the shell, hull.
Boat builders, may build their own shells but tend to only do the fit-out.
For instance my boat has a Jonathan Wilson shell and a Fernwood fit-out.
If this is your first boat, which I think it may be, then unless you have a lot of experience hiring etc. then I would advise against having your first boat built to your specification. Of course you could buy an off the peg new boat.
Take your time go and look at many,many boats that take your fancy, engage brain, not heart when you go and see one.
As said buying pre-used can save you a lot of money.
When you find one, come back and ask for our thoughts.
They may seem to be but that is the 'asking' price, when you have it surveyed, there may be some minor problems which may give you a bargaining point.
If you think used boats are over priced then have a look at new ones.
If you want some more guidance as to what is available then giving an idea of your budget will help.
Do you have, £25,000, £50,000 £75,000, £100,000 or more