The problem I see with people doing these cost analyses for home or car DIY repairs is that they always compare two simple things: 1) the out-of-pocket cost of the professional job vs 2) the hourly cost of the DIY job, plus parts and materials. They completely forget to account for the cost of their their time in scenario 1.
Having your car or house fixed by someone else isn't that easy. Unless you have a personal butler, it's not like you just tell some person "fix this" in 5 minutes or less and walk away, then pay them when it's over. If it's a car repair, you have to transport your car to the repair place, then either sit there while they fix it or find some alternate transportation, then you have to come back after it's done. If it's a 1-hour job, how much time will you waste just traveling to and from the repair shop, plus potentially waiting around for it to be done? You probably could have done it yourself in less time. For a house repair, you don't have to travel there, but you probably want to stay at home while the work is being done unless the house is empty, or you really trust the contractors and sub-contractors. So in either scenario, there's a lot of your own time that's not being accounted for.
And this all assumes that the professional will actually do the job correctly, and you won't have to deal with issues from them doing it poorly. This could easily end up taking FAR more time than the original job. And in my experience, the so-called "professionals" frequently do a shoddy job or are completely incompetent (so now you need to spend a lot of time trying to figure out who to hire so you don't get screwed).
So in my view, if you mostly know how to do something yourself, it doesn't need a whole team of people to do, doesn't require expensive specialty equipment, and isn't highly dangerous, it's quite likely a better deal to just DIY.