For keeping SPS, I think light is one of the most important factors in maintaing a colorful and growing reef. I don't think going cheap is a good idea, especially if you don't know the PAR ratings or haven't done any tests yourself. Thank God for Sanjay Joshi and the results he has published. I would recommend looking at his data (sorry, don't have the link but I believe it's in the Lighting/Equipment forum). Since most recommend changing MH bulbs after 8-12 months of use, saving $10-20 a year for what could be sub-standard performing bulbs doesn't make much sense. I know the tried and true brands are a little more, but lighting is something I don't recommend skimping on.
Just my $.02.