If you find the right builder and develop a good rapport with him, you may find the experience of both the you have and the bike that results is enough that you will not regret the money spent.
I found a builder in Portland through a recommendation for a builder to build me a custom stem. Landed the job that paid enough that having the bike I had wanted since I test road an early Merlin many years before. Went to the builder of my stem, Dave Levy of TiCycles, with a quite specific idea of what I wanted but quite open as to how to achieve it. He built me a bike that his unique, felt perfect from the first ride. (Oh, I had to do the usual tweaking of seat position and bars and hoods. But everything fell completely within the norm, most at mid-adjustment. The seat set-back was an exception. I spec'ed a 74 seat angle to allow decent sized tires, rear wheel well forward and room for fenders. All to get the bike I REALLY wanted. That meant a good deal of seatpost setback was needed. First go-round, I used an Avocet seatpost and the seat slammed. Worked until the post broke. I ended up with a custom TiCycles post with tons of setback. Elegant, does the job perfectly (clamp no mid-rail, not slammed) and very expensive!
End result of this collaboration? Well I now have another TiCycles custom. They have done very significant repairs on two of my other bikes and built me custom drivetrain parts for my current project. All 5 of my bikes are significantly better because of this. I have close to a dream fleet of bikes now that are all a joy to ride and that I trust completely. I also have a bank account that is significanty lighter. It's a deal that works for me.
I'm actually not quite done. The Peter Mooney will get a badly needed paint job at the end of the summer. I'll have TiCycles do a touch of maintenance work, move a cable guide that now is in the wrong place (for reasons that couldn't have been anticipated 40 years ago) and add a third set of WB bosses under the down tube. (This will be the bike's third paint job. The second was at year 5 after a fork ending crash. Ed Litton of Richmond, CA, just starting out on his own, charged me way too little for a perfect Imron paint job. (There was one pinprick of an imperfection on the inside of the chainstay that I never found again after the bike was built up. But 25 years of life, moving and riding have taken their toll.
Ben