In the custom world, you NEVER come close to recouping your investment. I have thought about this exact project, but the numbers I crunched put me off. I did figure out that in many cases, you can buy someone else's custom for a fraction of what it would cost to build ...
This ^^^^ If you want to gain a perspective on custom rifle resale value, take a look at Hallowell's website below. Figure the cost to re-create some of those rifles in today's dollars.
Hallowell Custom Rifles For Sale