I would consider getting a three bulb bar light. They're usually made for bathrooms, and they're less than $20. Put three Y-sockets in there, and you've got 6 CFLs. That's going to be plenty for a tower. You may even want to go for a two bulb bar so you've got 4 CFLs.

Because of the small space, I would recommend small CFLs...not too small...just keep them under 40 or 50w actual watts. Using one big CFL sounds good, but it isn't any more efficient, and I think the ballasts get hotter. Go to Wal-Mart and get 26w 6500k Daylight bulbs for Veg, and 23w 2700k Warm Whites for flower. Including the bar light (and the plug you'll need get and wire for it), the bulbs, and the Y-sockets, you'll probably be out less than $50 for everything.