Not a valid comparison!
No logical person goes out to specifically BUY those tools!
They already own the tools, or they would not consider doing the job!
how do you think we got the ones that they already own?
Do I go steal or make a new computer to run the software that I also have to beg, borrow or steal? No, I buy it (or more specifically, I purchased it-same computer I'm using right now). It didn't just fall out of the laptop tree, unfortunately.
here's a good example. Still messing with this old Mule. I suspect fuel pressure is down. I have a gauge, however I don't have an adapter to fit these style EFI fuel lines. So hey, I'm kind of industrious, I'll just make one. Dig around my stash of junk and find an old fuel rail and an old pump, then an old line, and fabricated a new test line-so that my gauge will "tee" off of the assembly. Perfect. Unfortunately I'm on the clock, and 2 hours after the fact I'm finally able to accurately test the fuel pressure (30 psi-should be 40). Now Mr. Customer would generally get to pay 2 hours' labor plus the pump plus installation time. OR option #2, buy the gauge adapters for $59 and that will be a "shop supply"-that I eat, then charge the customer for the pump + labor, and use the gauge next time too. That tool is a tool, which is designed to save the customer a little money and decrease the amount of time that the techs spend in making stuff. BTW that customer is a farmer, and a good friend, so I didn't charge him 2 hours labor...that's just became a loss of about $300. Or I could have just waited & bought the $60 adapter kit. But ya know? Farmers can't always wait and downtime costs them too so rather than make him wait another week, I just did it for him-and ordered a fuel pump (which should be here tomorrow).
Look at it this way. I make a lot of my own tools, even for work. Seal drivers, installers, bushing drivers, etc--on my lathe, at home, on MY time. If I wanted to (and I could, easily) I could charge the boss for these tools, and he'd gladly pay it-but obviously passes the cost onto the customers incrementally, over time via "supplies" charges that everyone pays. In our case, it's a percentage of the total bill up to $50 maximum. That way if the bill was $3000, it's still $50, but if the bill was $100, the supplies charge would be about $9.25. Also covers shop towels, rugs, cleaning supplies, pens, paper, clipboards, and a whole bunch of other stuff that people never think about. Miniscule when it comes to big tools like tire machines, welders, etc.