As long as you aren't stealing geometry, I don't think selling the models would be a violation. The names might be trademarked, so you might have to give the items names other than what they are for the game. If you are worried, you could always write Bungie, tell them you are doing hi-res 3D models based on Halo and ask if they have any problem with you selling them. Doesn't DAZ sell a car model based on a real automobile? If they can sell a 3D model of a real vehicle, why wouldn't you be able to sell a model of a fictional vehicle? I don't know enough to say for sure it's legal and o.k., so investigate, but if it is legal, you should sell these, rather than give them away! :-)