Yes, I'll need a backflow preventer.
Yes, a decent pump is ~$100. You can get by on less like I'm doing now, but the shurflo pump I had was a $250 pump. It could have run 200+ nozzles. I believe in always having headroom so if I want to add enclosures/nozzles I'm covered. I'll be taking it apart to see if I can fix it.
Between the pond pumps for drip and the diaphragm pumps for mist, plus the backup pumps, yes, much cheaper to have the city pressurize the water for me and just control the flow.
Those with large setups will agree. It will provide much more options at a lower price overall, and lower maintenance. If you just have a couple enclosures, not so much. The only thing that stops most of them from doing it on indoor enclosures is the flooding hazard.
I could get by using a pressurized tank instead of hooking up to city water, but then I'd have to refill it, same as I do now, but I'd also have to pressurize it. I had a system like that for awhile that used a corny keg with a fitting for my air compressor. It was pretty slick, and silent. I still have a case of sprinkler timers and valves from my former caging/mist system business so my upfront costs would be negligible.