and the time is determined by the "book" and not by how long it actually takes.

replacing the brakes bads+discs for example .. shop is going to charge at least 4hr or going on $600 to do that job for you. meanwhile if you own a jack, a jackstand or two, and a few wrenches (bonus for electric impact wrench) you can do the job yourself in a couple hours.

combine with the parts prices from most shops (especially dealerships) vs ordering your own and there's even more savings. case in point.. VW Parts Dept. quoted $1400 for a new turbo. VW Service Dept quoted me $1900 for the exact same turbo. $500 to carry it down the hall I guess.
I ended up ordering the turbo from a 3rd party parts seller for $1000 and took it to an indy repairshop where labor rates were 25% less than the dealer.

oil changes are also easy to DIY, but pricing can be a wash (or only ~$20 over the cost of oil+filter) because of the deals regularly offered to lure customers into the shop