Sours are definitely cheaper to brew but expensive to buy because you don't pay for the time at home involved in making them taste delicious but you definitely pay for it at the store.
I typically find myself perusing beer displays and rather than picking up bottles to buy I often think, "I could brew something like that, no need to pay for it pre-brewed." It's probably really arrogant but I look at beers like typical beers with X fruit or spice added or typical beer style aged on oak and don't see why it's $15/bottle just because they ran it through a barrel for a few weeks when the base beer isn't anything special. I have oak I can add to a generic beer, too. Again, probably arrogant, but I'd have a lot more fun brewing it myself and spending less money than paying a lot for one bottle. I mean, $15 for a 750ml is about what I would spend to brew 3-5 gallons of the same thing.