18/6 and 24/0 are standard for veg, i use 24/0. i would recommend buying a light online, you can find the best deals for entire kits; it includes a reflector, ballast, light fixture and sometimes even a hanger. you can get deals for around $200-300 for a really nice 400watt or even a 1000watt if you look hard enough. my 1000watt hps was $350 for everything including switchable ballast. there's also local hydroponics/hardware stores that sell hps lights, but the best prices are online