What do you plan on keeping in the SW
tank? You can do FOWLR
(Fish Only With Live Rock) and you won't need that much to start with. Stock lights, sand, live/base rock, and a decent filter is pretty much all you need. You can start out with this and then see if you want to do corals in the future. Once corals get involved, you'll need to upgrade lighting (can get expensive), eventually get a protein skimmer, and make sure the tank has been running steadily for a few months.
Basically I'd start with a FOWLR
until you can afford and start slowly piecing a reef together. That's what I'm doing.