700 might be reasonable....for prescription progressive bifocal and good frames. And since you probably wear them pretty much everywear, is wel worth it.

100 dollar non prescription sunglasses, on the other hand, seem kinda expensive and if they aren't shatter proof, are putting your eyes in as much danger as the cheapo ones, possibly more.

I usually wear a pair of cheapo safety glasses which I get from work for nothing. They are even almost cool looking.