It doesn't have to be as expensive as some people seem to think, a lot depends on the choices you make when it comes to stocking etc. including buying the tank and stand, and the livestock, i got my whole set up done for just under £200.
People say you need a skimmer a lot, but i think it depends on the bioload and the size of the tank. My tank is a nano tank (a tiny salt water tank) so literally has one fish, one hermit crab, one shrimp and one snail, and the last three all act as a clean up crew to the fish. There is a filter inside the tank that keeps the current pretty high and just works in the same way a powerhead would (no filter material inside it, just live rock rubble), as you dont want stagnant water any where because waste will build up.
One big difference between salt and fresh is live rock. The little critters on and in the live rock will filter the water for you, assuming your bioload isnt too much. This can save a lot of time and effort, as you are re-creating nature to let the little guys deal with the fishes mess. I have coral too, supported by a £30 light above my tank, with glass over the top of the tank, and have my tank right by a window and the soft coral in the tank is doing fine. Not saying this would work for everyone (over feeding can lead to an algae build up) but my snail does his job well at keeping the tank clean.
In reality my tankis just live rock, filter, basic light, and thats about it! One thing i would say is dont expect to get as big a bang for your buck as freshwater,and dont scrimp and save... get a refractometer rather than a hydrometer for example, the extra accuracy is vital when you have so much invested in a tank.
Keep your head up, it can be done cheaply, as long as you dint mind the cheapness dictating what you can and cant have in your tank.
Edit: have a heater as well of course, but somehow forgot that!