Rolls of thin sheet aluminum can be obtained at Home Depot for about $5 - $15. More than enough to make a nice reflector. Wear gloves when working with that stuff, it can give a nasty cut.
Here is a common design for a reflector. Two half circles of sheet metal. The red dots are where the bolts would go through. By bolting the outside of the semi-circles coser than the insides, you make a cone shape. This can be mounted with a bracket, to attatch to your socket & bulb. Ble dots are where the bracket would attactch to the main reflector
With hommade reflectors, I suggest taping the edges with duct tape to avoid cuts
Good luck
