For one plant, you can get 23-42 watt compact fluorescent light, 6500K
color temp. They have them at Wal-Mart, or any hardware store like Lowe's or Home Depot. I've only ever seen up to 23W at Lowe's or Home Depot; but I found a 42W 6500K TCP compact fluorescent at Wal-Mart. The more watts the better like Adam said, but a 23 would do. Name brands like Sylvania, GE, TCP or Philips are best; just don't get a no-name brand or store brand as they don't push out near as much light intensity no matter what the label says.
Keep it about 6-8 inches above the plant; too close and you can burn the plant's leaf edges, too far and it won't get enough light since the light strength of fluorescent light decreases exponentially with its distance from the plant. ~14 hour a day light cycles. Replace every year
; the light might look the same to you after a year, but believe me your plant can tell the difference.
E.g. Something like this would be a very good one and it's only ~$12 plus shipping: http://www.1000bulbs.com/42-Watt-Compac ... ents/1086/
Or you could check for it at Wal Mart of a hardware store.
A similar-to-above 23W would be fine, but the higher wattage bulb will support better growth and coloration.