Re: sorry, this might seem dumb....
Max Cottam at Cottam guitars can insall a new fingerbaord on your existing neck if you want a fancy inlay or something, and many luthiers could do something similar, such as a nice plain piece of ebony etc etc.
if you want a whole new neck, the 'bay is your best bet. you could buy the guitar with the nck you want, swap them over then resell the "other" swapped over guitar there straight afterwards.
Other than that look at local luthiers pricings to see what you call "expensive" iswhat they call "expenisve".