In reply to fifth:
with regard the cheaper stuff i've been using Bloc sunglasses from TK Maxx for the last few years.
normally pay about £15 for them (without case or bag)
and a cheap and cheerful set of "swopable lens" glasses from argos for mtbing
used to wear oakleys, can't afford to replace the lost ones anymore. oddly i've been less clumsy / forgetfull since using cheaper ones