HPS is high PRESSURE sodium. It's the same orange kind of lights they use in parking garages. You can get a really cheap 400watt system for $125 but that's what I did and the ballast burned out in a month. So I would save $250 and get a really nice one if you eventually go that route. The difference in my electric bill last month from the bill for June 07 was $13 with my 400 watt.
Just know that HPS makes a lot of heat so you would then need to spend more time and money on cooling your grow area. So it depends on your budget and desire to grow. Any fluorescents you add now will not go to waste if you eventually get the HPS. At that point you would be able to keep a set of plants in veg and another set in flower, which if you're into it enough to get the HPS will be something you want to do.
Why don't you start a journal? You can put your link in your signature like mine. I would have failed miserably without the help I got in my journal. You can tell because it's about 100,000 pages long, lol. Just go to the last few pages to see the where you could be in a few months. Let's just say I'm pretty syked about it.
So I wrote a lot because this
just keeps burning... and burning... and burning. Hopes some of my ramblings help and/or make sense.