Having worked as a general handyman for the last 6 years, and having taken advantage of other people thinking the same way, I am inclined to disagree.
We (technicians) don't know as much as we like you (our clients) to think. We have a general understanding of how mechanical things work, and maybe a set of common problems we have seen in the past, but a whole lot of it is just taking things apart, looking at them, and figuring out what is wrong - and sometimes trying things until something works.
If a specialist can diagnose and solve the problem in 2 hours, you can probably do it in 3.
If it takes the specialist 8 hours, he is gonna charge you a lot more than $500 in parts and labor.
Because our time is valuable too! We charge for the parts, and then enough to cover the hours, the mileage to drive to your place, whatever company overhead, and then end up with profit to tuck away for retirement.
Just like BenDar, I had a client who took her van to the dealer because the side door wouldn't open, and they quoted almost 2 grand. She asked me to look at it instead. I took it apart, found a faulty $20 motor, (and charged about $100 for the labor to diagnose and install the new part).
Besides, whatever time the tech is working on it, you can't be at work, and you can't be at the park with your kids anyway, because you have to be there to let the repair person in.
On the other hand, if you do it yourself, you don't necessarily have to do it all in one go, you can do a little here and there when you have a free moment. And in the end, the skills you learn will make it that much faster to do the next job. Actually, that's how I learned to begin with; just doing my own maintenance, and then doing it for friends and family, until I felt confident enough to charge strangers for it.
But wait a moment... $50 real wages? Unless my math is way off, if you are working full time, that would be nearly $180,000 a year salary. Well heck, with that kind of income, sure, outsource all your labor, why not?
Especially if you live in the SF Bay Area. I have good rates ;)