Well, you don't really need more than about 1.5 or 2 watts per gallon to see your fish well. Obviously, it's not all about watts, some of it is about the length of the bulb. A 24" and an 18" bulb don't really cover your tank with light.
The bad news is that lighting gets expensive
Big Als has T5 strips for about $45, that will give you 42 watts, but it will be brighter than what you have (it's a Coralife fixture). If you really want a lot of light, you could look into this fixture, which is really cheap for the amount of light:
http://www.aquatraders.com/index.asp...ROD&ProdID=144 I have heard reports of problems with that site if there's a problem with the light. I have a compact fluorescent fixture from them that works fine.
Big Als also has a twin standard fluorescent (would be a total of 60 watts) for $72.
Both compact fluorescents and T5s will give you brighter light than a standard fluorescent (T12).
You might find a good deal on eBay, if you're lucky.
If you're handy, it would be pretty easy for you to build a hood, get some ballasts and wire up some bulbs, but it does need someone who's into DIY. It still won't be that cheap, but you could probably do it for less than a standard fixture.