The Barr report is a very good site. I agree for the most part that K rating is up to personal preference, this goes for basically anything from about 6,000 -10,000K. However really low/high K ratings have always done weird things for my plants. I have some bad (IMO) bulbs on a 15gal, 2wpg and can barely manage to grow anything. A stock 18,000K(maybe 10,00K I can't remember) and a 2,800K bulb. Dunno whats up with that tank, even java moss has a hard time. Also considering I run 2 different hi-tech tanks at 2wpg and 2.75wpg using what I consider good lights and can maintain a dense jungle.
is a thread comparing different K ratings. Also showing my favorite bulb, 9,325K ! Plants and fish look great under them. My other tank w/ 6,700K always has this green undertone on everything. Annoys me to no end.
If you want to go really cheap for light, go to home dept/any similar store and hunt for some good spiral compacts, some double socket fixtures, wire, sheet metal(or tinfoil if you are cheap) and some wood. I build or modify most of my light fixtures.