<Giggle>LOVE that one</Giggle>
Figure a budget... and then figure you're going to blow that budget

That big, expensive glass box? By the time you're done, the cost of that glass box isn't even going to be a major percentage of what you will spend on a full blown reef tank. Costs grow exponentially with size. Lighting a 24" tank? Easy. Buy top of the line... you only need one. Lighting a 6' tank? Multiply by 3. Now, that top of the line, $400 light doesn't look so attractive. Even simple stuff... water changes. I go through a 55lb box of salt every other month... and by the standards around here, my tank is medium sized!
Here's my list:
1) Research. You're here, that's a good start. Check out BRS's 52 weeks of reefing series. Look at the different 'systems' that vendors offer (Triton, Red Sea, Zeo-vit, Aquaforest, etc). Evaluate those systems against your goals. Understand how they're working. I'm not suggesting that you pick one... though that's not a bad plan, but even if you don't end up using any of these 'systems'... knowing and understanding them will better enable you to design your own system. Don't buy _anything_ until you know what it is that you're wanting to achieve.
2) Buy used. Turnover in this hobby is huge. There's _always_ some poor sap that spent a bundle on a brand new system, figured out just how HARD it is to really get the kind of results they wanted, and is ditching the hobby. Even among successful reefers, the upgrade bug is strong. There's literally TONS of good, used equipment out there.
3) Take your time: The number one resource consumed by a successful reef is time. You spend the time to learn, the time to select the proper equipment, the time to pick critters that can coexist in peace, the time to maintain, test, clean, and just plain observe your tank. If you can't invest the time, don't invest the money... Unless you can afford to go all the way and hire an experienced maintenance company, you just can't buy success in this hobby.
4) Have fun! This is a hobby. You want to look at a gorgeous reef once in a while? Buy a season pass at the public aquarium

A hobby, by definition, will consume as much of your available time, energy, space, and money, as you'll allow it. If you don't enjoy the process, what's the point!