I am using a 250w ballast from htgsupply with a 250w cmh bulb. I have been running 2 weeks now and it is going great. The ballast I bought is the agro star from htg, it is like the middle priced one. BUT...... this ballast and the cheaper one they sell are just cheap Chinese made ballasts, the coils in them are not even copper. I learn all this after I buy it btw. The ignitor in mine is weak as well. It fires the bulb fine, but I have been told that it will not last long.
I got all this info from a guy at Advancedtechlighting.com. He was very informative, and is even sending me a new, upgraded ignitor. They sell 250w ballasts kits and the bulbs on there site. There ballast kits are only like 50 dollars and supposedly made from all quality components.
The reason I went with the htgsupply kit is because the reflector that came with the agrostar ballast was perfect for the little cab that I am using.