huntsman-
I don't know where exactly you are in SA (I have good friends in Malelane, I love it down there) but I'm pretty sure that specialty items such as HID lights are pretty expensive relative to standard flouro fixtures. And since you're down there and only need the lights for seedlings (lucky!) I would say you'd probably be best off by just adding more flouros for the time being- if later on you get sorted out then you should look into something like a 450 watt MH. I've had great success using 4 and then 6 each, 4' flouro tubes for starts. Get some Philips plant light tubes or equivalent, wire 'em in with your current fixture, and you're done. It's easier, in my opinion, to mount the lights on a board that can be raised or lowered than it is to build or buy adjustable shelving, but you will definitely have to do one or the other- since you're basically poorboying it you absolutely MUST keep the lights very close to the plants to keep them from getting too leggy. Also, surround the plants with mirrors or mylar or some sort of reflective material to maximize the light.
Good luck, post pics!