I think the first thing you need to do is decide what kind of corals you want to keep. A 55g tank isn't going to need 2x250w MH
bulbs. If you are looking for a complete fixture I would look at one that is 2x 150 with T5s not CPs. There are tons of options out there for exactly that. As has been mentioned you want to check the brand you are buying. Cheap usually means cheap. Lighting is one of the areas in this hobby that is going to cost you.
So...my recomendation is:
1. Figure out what kinds of corals you want to keep(2x150HQI MH
w 2X54wT5 =408w) or 7.4 WPG
. You could keep just about any SPS
2. Look into a fixture that uses T5s rather then CPs