I have had and currently have several different types of lighting over my tanks. Over my 125g I have a 12 bulb t5 fixture which is doing a pretty good job of growing my corals. Only downside to t5's is the bulb replacement cost in my opinion. Another option are the led
panels you can get on ebay or amazon. I have one of those over my 60g cube and it's very very bright. No bulb replacing either and they last about 10 years or so.
metal halides are still great lights to use but you can have heat issues and still have to replace the bulbs every year or more frequently depending on use.
T5's and LED
's will run you about the same amount pretty much, give or take $600 or so. If you have a canopy the led
's would be awesome cause you could hang them in there. The T5's are great for a non canopy tank like the one I have.
Hope that helps a bit!