what's the best lighting system
 

what's the best lighting system considering cost as the first priority?

I would go with a 400 watt High Pressure Sodium or Metal Halide. I found three 400 Metal Halides at my local flea market for $30. apiece a few years ago. Those orange looking street lights you see in parking lots are HPS lights and Metal Halides are used in large buildings. Next time your in Home Depot look up and you might see them. You can start with a 250 watt if you are really on a budget but I would stay away from florescence lights because of the cost per watt of using them. They are only good for the first few weeks of plant life then they need more light.
Ron