I think some posters here may be missing the point. I understand there are misconceptions about SW tanks however, what I am trying to get across is, even considering you don't need corals, you don't need live rock, and once it's set up its "easy" I have a few problems. The first being the fact no one has mentioned that a SW tank without live rock and corals is lame lame lame! Also (personally) I'd want a big tank, I wouldn't want a small 30 gallon or something. So if I wanted to start it up, I'd want to go to the LFS and buy a TONE of fancy cool corals to cover the tank and live rock. Man I could spend £500 easily on that, then theres the fish, the tank, the skimmer, salt, RO units, the lighting for the corals its MUCH more expensive stop kidding yourselves on! And the whole thing is much more delicate to if you keep corals. Lighting goes out for a few days or the bulbs blow on your tank when your on holiday you could come back to everything dead in your tank, at least if this happened in FW it's cheaper in general! The fish cost a fortune for the really cool ones (personally I'm more into amazonian and indonesian FW fish but go figure). I'd still consider it one day.
It's so much more hassle so stop kidding yourselves. I'd also want to have an RO unit also, unless I want to have water sitting around the house everywhere with salt in it, or having to cart big drums of water from the LFS once a month. I'd also need a good skimmer.
I could go out tomorrow and buy an 8FT tank for under £1000 with some cool FW amazonian fish that get huge and colourful and stick the FX5 on it i already have with another. I'd like to see that happen with SW...it's just not realistic.