I have had three guns fitted - and it doesn't need to be all that expensive. There are several things you have to consider;
1. Do you have a present gun/guns that can be adapted?
2. Are you happy with extension pads (e.g. ebonite/walnut extensions)
3. Have you found a good fitter you can work with (and it is a partnership).
On the first point, a gun with adequate length and no internal stock bolt is ideal. A gun that is already a bit short and/or has an internal steel bolt is harder - but may be possible.
On the second point, IF you need a gun longer - and you are insistent on having one piece walnut, they it will be expensive - however, a leather covered pad, a Silvers pad - or even ebonite are all alternatives.
On the third point, you need to be mounting the gun consistently and have a consistent style. You then work with the gun fitter, very possibly using a 'try gun' to get the dimensions you need to make the gun just drop naturally into place. Its not rocket science, but it does need both consistency from you - and a skilled fitter who can see when you are mounting 'naturally' and when you are making unconsciously adjustments for the fit of the gun as it is in your hands at that instant. That is why a 'try gun' is useful.
There are three books, Mike Yardley, Rollin Oswald and Arthur Hearn all of which give good information, but none will actually enable you to 'fit yourself'.
When you do get a gun right, you will wonder how you ever managed without it!
