Don't buy NO (normal output) T5s!!! I am always tempted to buy those aqualight 20" fixtures to throw on little 10 gallon experiments, and then I remind myself that they are pretty much worthless. You didn't mention a price, but if I recall correctly, they would cost me $28 and change wholesale.
Here is the thing about light...you can't have too much of it. Seriously. You simply can't come close to approximating the strength of sunlight.
Light is no place to skimp. Spend the money now and get a 150w Metal Halide. Try craigslist and you can probably find it for $100. It will save you the trouble of buying one later. Everyone does.
Basically, with corals, increasing difficulty of care involves increasing light (until you get to the most difficult-to-care-for corals which are ahermatypic, meaning they lack zoanthellae and so need to be fed). When you find out you can keep easy corals, you are going to want to keep harder one, and so on... Instead of upgrading the light three times to reach the MH, why not just start with it?
