This was a very timely thread that reminded me that I, too, need a pair of polarized sunglasses.  My old sunglasses are prescrips and really old plus they are not polarized and therefore, useless on the water.  So, of course, I researched the hell out of this and decided, first, to go with copper tint.  I also discovered Kaenon sunglasses, which of all the brands struck me as the best quality.  I read a lot of comments from Costa people who switched to Kaenon but none going the other way.  Anyway, Jax, if you're still looking you might as well have the benefit of some of the excellent deals that I discovered.
Take a look at Kaenon first.  Here's the pair I bought:
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And here's another style at a good price as well:
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And these:
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I chose the Kaenon Burnys because I want a pair of sunglasses that really cover my eyes, especially the peripherals.
If you are interested in a pair of Costas these are a good price:   (You need to Login or Register
Sierra Trading Post is also clearing a lot of Serengeti models but in the end I was sold on the Kaenon lens technology,which is exclusive to their glasses.  Family owned company, very high quality and apparently very big amongst the sailing crowd.
Good hunting, Jax.