I wish I could chop & change, but as I need prescription lenses, Oakleys come in around £230, and the frames kept breaking, which was fine while they replaced them under warranty, but now the new 'fives' frames are a different shape! I had prescription serengetis about 15 years ago, they were great but staggeringly expensive. Plus when your prescription changes you have to buy new standard glasses *and* new sunglasses! My Oakleys and Serengetis now sit gathering dust in a drawer.
Flip-downs over standard glasses are just too uncool to think about.
A helmet with tinted visor only costs about the same as a few sets of sunglasses and will last several prescriptions-worth, but can cause some unwanted attention when worn around the pool or in the car, so it's not a real substitute for general use...
Just another expense to add to a pilot's list!
BW