Relamp and retrofit your fixture with T5's . The T12s usually supply a 34w or 40w lamp. The T8s supply a 32w. The T5s use a 54w. Plus, the T12s can run off an old school magnetic ballast (ie. energy consuming whore), but about 3 years ago mfgs finally started making electronic ballasts. It'd be better for you to get the T5s (even though they're quite a bit more expensive) because they last an average of 20,000 hrs as opposed to its T12 and T8 cousins which only last an average of 10,000 hrs.
As for plant lights, over the years, I haven't sold too many of them. Most people grow well with regular fluorescents with 5000 or 6500 kelvin and do just fine. Now, with aquarium lights...the price on them is just outrageous. About ten years ago, as a specialized lighting distributor I paid $20 as my cost for just the 2 ft ones, but the aquarium stores were selling them for $40+. Personally, I don't know how well the aquarium lights work for growing plants but I'd give it a go if I could get the lamps for free. Although, keep in mind the kelvins are usually rated around 10,000, which is considered extremely blue in the colour spectrum.