I tried the cheap light method last week and the weight of the fixture plus bulb had it way too close to the water. I would up spending more and getting a JBJ nano glow because of the way it would attach.
You can go the cheap route though, I read a million threads about it before I tried it but you will need to rig it up carefully. From what I read if you get the right type of bulb you'll get good growth. I spent less than $20 for the fixture and bulb, certainly more affordable than the $55 I wound up spending.