well not always. My T5 setup for my 120 didnt cost more then 500 bucks, and thats a lot more lighting then you will need. My setup is 8 T5HO bulbs all with individual reflectors, which is the make or break factor for T5's. I am running 2 IceCap IC660 ballast which instead of running the average 4 bulbs at 52 watts or whatever it is, they are over driven to about 85 watts. The bulbs can handle this but it does lessen the life on the bulb which means they need to be replaced almost 18% sooner then normal. Not a huge number but enough to make a difference in a SPS tank. For your set up I would do some shopping on several websites and find the set up that's best for your needs. I would go at minimum 4 T5 HO bulbs. The reason I would like to see you do a retro kit is because most fixtures will only have modular reflectors, which are bent to be "individual" but not as good as ones made for retro kits so I think its a waste of money. Retro kits will be more efficient at transferring light into the tank, which means you can get equal results with less bulbs because the PAR is higher. The higher the PAR the more versatile your lighting will be for all corals, including SPS.