FWIW
Mike I agree...at least that's how I was thinking when I started. I invested in me. No business plans or expected monetary gains.
As for the "size" of the investment. Well that's all relative I guess.
There are many ways to do things - different costs for different tools. I sure didn't invest in a CNC to make necks and one for bodies so I could have repeatability on hundreds a whack. lol. I settled for a router table and file.
The real deal is that when one takes on building rather than assembling by parts or kits it pays to do the homework before investing. One may imagine; How many people in factories do specific tasks to build an electric guitar? Then realize that you need to be able to perform each task at their professional level. Well each one of them do their thing 8 hrs a day...no telling how long they've been doing it and all their supplies and tools were paid for.
I know I studied for a long time and made decisions on how I would attempt each task and the tools it would require. When I could build the guitar in my head is when I decided to give it a go.
It was a minimum investment. Nut files and Fretting tools. I had a selection of power tools good enough to see how things went...on my patio.
My first build was a neck-thru design and I had been spending time checking out the workings of Carl Thompson.
Well that guitar build was worth my investment...including the cost of building a 24' x 30' shop and many, many more specialized tools. It is in a display case on the wall in my shop and I wouldn't be ashamed of any guitarist to check it out.
That was seven years ago. I've since built many guitars and absolutely love seeing the faces of the pickers when they receive them. Of course many where shipped so I didn't get that...but no doubt- it was an investment in me and still enjoying the thrill of not only the process but when the guitar is plugged in for the first time...that's when the story is told and it says it all. Only one way to know that story.