I'm in exactly the same situation, if your tight on money, start with a 18w flouro I don't think it should cost that much, i'm in england and it cost me £10 ($20) but it should be cheaper if your in the u.s

Another important thing is to buy
second hand I can't afford £180 ($400) on some crazy hydro lights. I bought a 150-watt Metal Halid lamp for £30 ($60-65) on ebay which was a bargain but have a look on ebay or locally.
When the plant gets bigger get some decent lights, how much watts is your flouro at the mo?