Low cost, Mars Aqua led from ebay at about $100. It's a well made fixture and makes good spectrum for your corals.
Spend quite a bit more to get more control like sunrise/sunset, moon light & 6 channels od color control. The best value here is probably the 24" Reef Breeders Photon V2+ for about $400.
All the extra control and expense is for your benefit as something to play with, it makes next to no difference at all to the corals.