Judging by the price you've been quoted, sounds like you're referring to the lens of the headlight which you can't find replacements for. If it is just moisture inside, drill a hole or two in the top and the bottom (of the back of the housing) which should help eliminate moisture build up. If the front cover is yellowed/foggy looking. Hit it with some 2000grit wet and dry, then polish over with a rotary/orange pad/plastic polish a few times. Then use a sealant/wax over the top.