There is a "sweet spot" for maintenance and size, and it varies depending on budget and time. "Medium" sized tanks from 40-90 can have most of the water parameter issues fixed by regular water changes, which is the cost of salt and little else. Smaller tanks are harder to maintain mineral levels due to smaller water volumes. Corals quickly deplete, and water evap causes fluctuations.
Not saying small tanks are impossible, or that medium sized tanks can be cheap always. Nano tanks require an expert and a reliable automatic top off....controllers for chemical dousing are a great idea. Larger tanks can have their dirty water replaced, but it gets expensive and time consuming mixing 40-60g water changes every other week.
My goal was to find that happy medium (because I am lazy), and I think that 40-60 is a great spot. My 40 gallon is my personal favorite tank. 10-15 gallon water changes/week are simple. There is plenty of space for rock work and biological filtration. My 90 on the other hand is just getting into "absurd". I am no longer operating out of 5 gallon buckets, and now have to mix water changes in larger vessels. To keep it simple, I do bi-weekly of 40 gallons. You start making things with pumps that will break. I have it down to a science at this point....However you can't just talk about this stuff in public, they think you are insane. Most people think a 20 gallon fish tank is large. I use a 40 just to mix for water changes. People can't wrap their head around the hobby.
Overhead costs are part of ownership, and we can't be fooled by the pretty pictures. Every stupendous tank has a closet or room full of buckets, jugs and pumps and likely another tank or 2.
@Polly
That deal for the 40g sounds really good actually. Good luck, and do let us know how it goes!