We live near a coast, so we could buy from a local fish store (LFS) natural saltwater (NSW), or artificial saltwater at $1.00 per gallon, or make it ourselves from RODI water and a salt mix. At this time, we use Reef Crystals for our salt mix.
We do a monthly water change of 25 gallons, or about 15% of the system water volume.
Budget: $12 for the salt mix. 1.5 to 2 hours including a sump tear down and clean out and a clean-up of the devices in the sump. Detritus, nuisance algae, slime.