go to a pet store and buy a 10 gallon incandescent hood, then put in 2- 15 watt compact florescent daylight bulbs in it (can be bought at kroger, the ones with the blue label) and put the light fixture over your tank
You can get a Current satellite 20" 40w PC fixture with a moonlight for about $50 new, but it comes with a 50/50 bulb and you need to replace it with a 6500k bulb, so that adds cost.
Heck, I have one I could have sold you cheap when I was back there, not going to use it now that I have a 150w Viper MH for my 30 cube
I could probably ship it to you fairly cheap, it has a new Sunpaq Dual Daylight 6500k / 10,000k bulb in it with about 2.5 months use.
nova extreme has an 18" t-5 fixture, but it comes with 1 20W 10k bulb and 1 20W acitinic bulb, so you would have to swap out the acitinic for another 10k (they don't carry any other types of bulbs for it yet since it's meant for saltwater).