The only thing I'd be wary about when purchasing from electrical supply houses is lack of detailed information on the bulb. A lot of Metal Halides can have less-than-ideal color temperatures, so if you go that route look for a Metal Halide between 5500 and 6500K, and an HPS that's 2000-3000K.
The Son Agro bulbs you are talking about are 430W, I have heard they work fine on 400W ballasts and I've also heard they might need a 430W ballast (neither sounds possible to me!) but I really don't know, as I have never used one and just the idea of a horticultural MH bulb being a bastardly number such as 430W makes my head spin.
I have used Sunmaster Cool Deluxe MH bulbs (MH conversion actually), and Hortilux Super HPS bulbs. I love both.