I wear prescription, blended lenses glasses and was looking for sunglasses that would fit over my glasses......Our local fly shop recommended "Cocoons Fitovers" with the low vision (brown tint) polarized lenses....this was an excellent solution.
You need to find a retailer who carries these sun glasses in order to make sure your glasses fit inside the Cocoons....they make several sizes and styles.
I paid about $40 several years ago.....beat them up and they still works great.
The low vision tint works good for streams, rivers and lakes here in Oregon.
Yes, with perscription lenses you can easily be looking at $500-600 for a pair of sunglasses. Always thought the Cocoons always looks "clunky" and heavy. I have found another manufacture that make a more streamlined fit-over sunglass with a much higher quality lenses. They are call Fit-Overs.