Well, a 400W HPS system is available on ebay for like $99. It comes with a batwing reflector. An air cooled hood needs to be bought seperately if you need one.

In my experience, a switchable ballast is damn nice, but you can get great results with a 400W HPS.

I get .36g/W using hydro under a 400W HPS, netting 5+ ounces/harvest and I am a total fuck up. Not bad for the wattage.

But, if you can afford a switchable ballast and the 2 bulbs, by all means go for it.

Good luck!