Actually halogen lights are really a bad idea, the coloring is way off from what our animals need to survive and the heat they produce would be next to impossible to deal with. Halogen's lifetime are VERY short, not to mention the colors will shift rapidly with age. Least of all the amount of electricity they consume will amaze you, sure you may get 500w of light but you also get about 400watts of heat per bulb. The only thing useful in them I see so far is maybe the enclosure, maybe the reflector, and the endcaps. (going to hack one to make a 70w MH pendant)

Now if you are really looking to do some off the HD shelf you type of stuff you can find HPS (high pressure sodium) fixtures to hack on that are a little higher color temp that may work for you for around $30 or so, they will be quite yellow. It's been done before successfully, I think Peregrinus still has a tank setup that he's using them on.

But from the sounds of it, we have another DIY junkie on our hands