if they are cheap style plastic lenses, use a product called Plexus on them. its a perspex/plastic polish and its brilliant stuff- not only for GA windows, but for cheapo sunnies and getting minor scratches out of CDs!!! its almost as useful as WD-40!
That option would cost me far more than I pay for my sunny's.
the cheapest option for me is to just get another pair.
The ones I get are pretty good quality, and quite scratch resistant........but I'm a real bully when it comes to glasses and can wreck the best of them pretty quick.
