You'll need a couple of powerheads to circulate the water, want a little bit of ripple at surface of water to aerate the water and help regulate pH. The powerheads don't need to be expensive; Some people swear by certain brands, but I just got the Petco brand for 2 of mine and the other is a maxi-jet cuz it was on sale and cheaper at the time. I've had no problems with those powerheads. Save money where you can, but spend it on the important stuff, and buy what you want the first time so you don't waste money buying a second item of the same thing (like having to buy a better light cuz the first one not good enough). For me, getting a good filter and skimmer was important, so thats where i spent a good amount of money. You don't need an airstone or anything like that, if thats what you're asking. Only things I have on my tank are 3 powerheads (I have a 55gal), filter, skimmer and heater. Oh, and light of course.
Getting a SW
tank going is expensive, but once you start it's so much fun!!