I’m not even interested in owning one (that’s what I tell myself - MTS is real), but how much does a budget saltwater nano (15 - 20 gallons, because that seems popular) cost for setup and monthly running?
Let's say you do a 20 long, and you don't take advantage of sales, and you have a relatively high amount of maintenance due to a decent stock.
Tank - $40 Aquaclear 70 - $50
Koralia Nano 425 - $29
20 lbs of live rock at $3 per lb - $60
20 lbs of aragonite - $20
160 gallons worth of IORC salt - $55 RODI filter - $150 (price varies WIDELY depending on the unit you choose to suit your needs)
Black Box LED lighting - $150 (again, this depends on the specific light you choose. $150 is a fairly common price point for the mid-size black boxes, though)
That doesn't include livestock, but should give you an idea. These tanks are pretty expensive, but aren't as expensive as a lot of people say. Admittedly, even just a couple of 10 gallon saltwater tanks leach a large majority of my "fun money" (whatever is left after bills and savings), but I get a lot enjoyment from them, so it's worth it for me.
Local hobbyists, mainly. No stores near me actually sell live rock - it's either the Real Reef Rock (which I suppose is live, but I've got my doubts about it) or dead rock. I've always either bought dead rock or bought from hobbyists, and I mentioned it in my head but forgot to type it out lol.
Basically, I'd buy dead rock, cycle it, and add your own pod population and such later down the road. Less chance of pests that way. But, if you're buying live, do your best to buy from a hobbyist. You'll usually save quite a bit that way.