Theres a thing on this site called the "growfaq."
It gives all the answers to questions like this one that have been answered 1000 times before.
Might as well make it 1001 though.
The best light source for indoor flowering is High Pressure Sodium lighting (HPS). The next best thing would be a Metal Halide. Both of these are HID lighting that require the use of a ballast. Neither of these are (usually) available for less than $50, however I purchased each of my 150w HPS's for $25 a pop. I should also note that HPS and MH generally run hotter than the next option.
If neither HPS nor Metal Halide is available to you, you can use Compact Fourescent Lights (CFL's). CFL's will get the job done, and youll still have some killer weed, but you wont have nearly as much of it. Id say CFL yeilds are around 30-40% of HPS yeilds, if that gives you any idea. Quality is still just as good as HPS, just less quantity. CFL's have their drawbacks, but are a good option for growers confined to very small areas, or growers on a very tight budget. My first grow was all CFL's. 16 females, harvested 7.5oz dry weight. I expect to harvest the same on my current grow, with half the wattage using HPS, with only three plants.
CFL's are also great for vegging. The best thing for flowering is HPS though.
