I totally understand the high overhead aspect, but I assume knowing what you're doing is supposed to help immensely with that.

Pride in work is a big thing. As someone who works at a desk, some manual labor on the weekend is a nice change of pace. It's also not pointless exercise. And in my experience the best way to get something done right is to get free advice from the pros and do it yourself. Because the people the pros hire to do it won't care as much as you.