It is rater expensive proposition but not because of keeping the water clean.
High intensity lights are not only expensive to buy and run, but also give away lots of heat. You need chillers to take all that heat away.
At firsts I had chillers that would throw heat into the house.
Good in winter, but in summer AC was running 2x.
I was dreading when was a time to pay electric bills (they charge extra for heavy use).
In places short of water, another consideration may be that to make RO water, only about 1/4 of original water makes as RO water, the rest goes down the drain.
With salt water swiming pool, I imagine, only
heavy duty filters/ skimmers,
UV light (antibacterial)
This is the easy part when looking at if from salt aquarium pov expenses.
Definitely much healthier the chlorine/bromine based water.