After breaking a pair of Spotters (my fault), leaving another pair somewhere and then losing a pair of similar Mako's to the bottom of a lake when I fell off a SUP (albeit all this over about 15 years so not too bad going), I've gone looking for cheaper solutions. Also got sick of the weight of glass lenses when cycling - nothing stops them sliding down my nose when I've a sweat up... or I'm looking over the side of a boat on a hot day!
But then my stand in wraps I bought from a servo lasted all of five minutes before the frame broke so that's not a solution.
After significant research on Australian and international standards, I went for a pair of UVWraps wrap around sunnies from Bunnings. Fully compliant with all the latest standards for UV protection (including at the right level), 99.9% as clear as the Spotters penetrator lenses I used to have (these are pretty good...), much lighter so they don't slip, fully polarised with orange high contrast lenses (great for a day on the water) and fully compliant for impact protection too (I also ride a motorbike with the visor up in summer and glass lenses are not the best idea for impacts). A nice grippy material behind the ears also helps on the ones I have. Reasonably robust and stylish too, although I'm not trying to impress anyone either. The only downside is the potential for scratches so just have to be careful on that front.
But at under 30 bux per pair, if they get scratched or I have to get a new pair every year, I am still well in front. My new favourites...