I have a Eureka lemon tree in my north/east facing apartment. I currently have it in a small greenhouse with two compact fluorescents giving it some more light (the only natural light it gets is morning sun). It has been doing fairly well, and was even happy enough to put out a lemon, the only problem is that since they are the compact fluorescents, I have to keep them relatively close to the tree's leaves, and it is now starting to grow on just one side.

So, my question is this: is there another (cheaper) lighting alternative, or should I shell out the $300-$600 for a "grow light" from my local garden store? Any help will be great!

I have a large indoor tree that grows toward a window. I just rotate the tree every now and then to give the tree a more even look.

Are there signs that the tree is getting too little light?

I suspect they are "60W equivalent", so probably 13W fluorescents. If that really is what they are then you can do a lot better before moving to a $500 grow light. The box stores have move powerful CFLs like bid2win mentions. They are very easy to find up to about 42W and they will just go into an ordinary lamp so long as it doesn't have a cramped fitting or shade. Then they are mostly sold as outdoor lighting, I've seen up to 105W as a security light. Two of those would be enough for any single plant indoors. Watch out you don't fry it!

If they actually are two 60W fluorescents then the next move upwards is quire a big step since you already have 120W putting out maybe 8000 lumens. You can get really powerful compact fluorescents, up to 250W, but they are by no means something you can just plug into a lamp socket. You can get an array of fluorescent tubes, maybe 3 or 4 2x40W shoplights, or 4x54W T5. Beyond that, HID lamps are the best way to get 400W-1000W of light from a simple package.