You definitely need to decide what you want to keep in the tank first. If it's just FOWLR
than almost anything will do. If it's corals or anemones I would suggest a T5HO setup if you don't want to do MHs. I had very good luck with a T5 strip on a 30 long, had no problems with any corals I tried, although I did not have any SPS
There are retrofit kits for T5s that you can buy to put in your own canopy, or a ready to go strip. The 48" T5HOs are 54 watts, so 4 of them would allow you to have most photosynthetic inverts. As for bulb color, there is some personal preference, but on a typical 4 bulb setup 2 10000Ks and 2 actinics (420 or 460 nm) is a good start. The 6500K bulbs are not actinic, they are daylight bulbs better for freshwater tanks.
As far as cost, I think it's about the same if you buy a fixture or do it yourself. If you buy a canopy that will definitely cost more. It seems like the components are just as much as a completed fixture, but you get more flexibility doing it yourself.