Yamaha champ Headlight

All right so I bought a little 1977 80cc yamaha champ for cruising around town when I head up to college. Ya it looks pretty dorky but its a champ. The headlight is currently burnt out and the replacement is 90 bucks (not happening). I cant replace just the bulb because its a sealed light unit. Its a 20w and has 3 prongs at the back for plugging into the wiring harness. Any body have any ideas for a makeshift light on this thing??? Or if its possible to replace a bulb on a sealed casing

 

Put an Offroad light

 

So I made a light from radioshack. Bunch of leds in the housing designed to run off 6v. I have a positive and negative wire running off my headlight. The wiring plug on the bike has 3 prongs. The light turns on when i plug the pos/neg wire into two of the three prongs. Not sure what to do about the third prong. I don't want to fry anything. I am electricaly challenged