Cheapest way I garentee and you ALREADY have it! (I hope)

Tooth paste! Seriously! I used Crest for that minty fresh headlights, a towel, and some spit. (add some good ol' h2o if you dont want to spit lol)

Sure it takes 5-10 min by hand but its just about free, plus what else are you doing besides surfing the internets for VX p0rn?