If you like your Costas, they will install new lenses fairly resonable.
I have a pair of WaveKillers with the CR39 plastic lenses because weight on my nose was a factor. They did the same as yours, scratches. I had them replaced with the same vermillion color lense but in the new light-weight glass called 580 lenses. Just got them back a couple weeks ago. Great so far. Go to Costa Del Mar website and fill out the repair form that you'll find under the pull down repair. Good Luck !!