cheaper or not, you are comparing apples with oranges. If you truly believe you will save money in the long run and won't have to deal with calupera, bubble algae, aiptasia, mantis shrimp, or any other nuisances or pests that come with real liverock than you should choose to use dry rock.
You will miss out on the true biodiversity that real liverock brings in and there's a good chance you'll have to deal with those "nuisance" things anyways- and it's possible you will have a more difficult time dealing with them because your aquarium lacks biodiversity!
I'm an SPS reefer. I try and keep things more controlled in my reef aquarium than most people. I've had plenty of opportunties to redo my reef aquarium with sterile dry rock and I never will.
As a matter of fact, if there was a way for me to possibly bring some more fresh cured high quality liverock into my system I'd do it in a minute.
You wont miss much biodiversity when you hand pick a detrivore package.......at least not the good stuff.........snails,pods,worms,macro algaes etc. As for controlling things.......dry + hand picked editions is by far the best we can do.