First things first. Welcome to the site! You've come to the right place. Lots of really helpful people with lots of experience. First you need a tank. If you are looking to go 55, I would agree with the multiple suggestions already made and look at a 75 or a 90. It opens up your livestock options a lot. You can find some incredible deals on craigslist that fit in your budget (like my $200 90 gallon tank and stand that also came with a useless sump and substandard lights, but damn, $200 for a 90 with stand is still a great deal! Thank you, craigslist........). Then you need to look at equipment for your tank. The next essential component for a successful SW tank is live rock. For those on a strict budget, dry rock from places like marcosrocks.com or Bulk Reef Supply are a great alternative. Get that and seed with a few pieces of live rock from a local fish store (LFS). You will also need to look at getting a light, protein skimmer, sump set-up, powerheads, and a heater or two. In this hobby there are lots of alternatives, so do your research. You will also need to invest in a water test kit (API, Red Sea, and Salifert are all great brands).
One piece of advice people here gave me is that if you are looking to keep corals in the future, invest in the equipment at the beginning. Many corals are easier to keep than some of the fish we want. Investing in the right equipment from the start saves you money overall since you don't have to purchase things twice. That was an excellent suggestion, and one I'm still grateful for!