I would save up to at least replace your t12's with t8's or t5's, even cfl's. T12's are very low lumens per watt compared to all other floros. I forget who, but assuming you are in the US, either home depot or lowe's carries the t8 ballasts for half of the other store. Also you can go to the local habitat for humanity for bathroom vanity lights to get the sockets for cfls, unbeleiveably cheap. Just my thoughts though, good luck any happy growing.
P.s. watch close for a few days after switching the lights to insure no flowering, odds are against it but i have had some older plants start to flower when switched to 16/8 (was kinda high thought it was 18/6 whoops) but if you catch it quick it has less neg effect than letting it go.