I agree I think the retro fit would work out much better for you. Plus putting a light fixture in side a canopy... well I think it would be harder for the fixture to stay cool even with fans.
If you do a retro fit, you can get the lights you want, put them how you want. And it really isn't that hard. You can find all sorts of used equipment on the selling site here.
Go to the equipment forum, ask them to help you design your lights, what all you would need to look for, etc.
Plus going by the watts is not a very good measure anymore. Because of T-5s, Their watts is way different that watts of a pc, or a MH.