My first SW tank was a 29 gallon fish/live rock. It had a heater and a AquaClear 500 filter on the back of the tank with a standard light. I spent around $300.00 for it. It was cool and all, but before long I wanted more and changed over my 75 gallon Discus tank to SW reef. I have had the reef for almost 3 years now, and dont tire of it, always something new to find/look at. Not to forget that it is much easyer to maintain. If you want more than a few fish and live rock, you can add the price of a skimmer, a good light, corals, a test kit, and RO water changes every 2 to 4 weeks, this will jump the cost up to what Frank was talking about.
When you figure it all out, you might as well go to a larger tank.