I suggest just getting a shoplight with 2 four foot bulbs, either 32 watt or 40 watt bulbs and you will get better results than using cfl. It wouldn't hurt to get 2 lights for a total of 4 bulbs. You will save money you can put towards an HPS for flowering, plus get better results. CFL's are just too focused for more than one or two plants, or have very limited space for lights. CFL seems to be the new thing so everyone is jumping on the band wagon. I've done both and can tell you that the bigger bulbs give better results.
Otherwise you should be looking at at least 2 42 watt cfl's per plant, plus the cost of sockets and wiring. For CFL's I do prefer the 42 watt daylight ones. This is comparing what is available locally, I've never special ordered the bigger ones online.