IMPORTANT WARNING!
Buy cheap sunglasses and you can get into trouble.
Fake sunglasses may well filter out visible light and not UV. Normally, your eyes narrow in bright light, restricting the amount of UV entering. With a pair of ultra cheap/fake sunglasses that don't stop UV, your eyes respond to the visible light, so they react by opening up your pupil, letting in unfiltered UV in great quantities. That will probably lead to cataracts.
There are plenty of cheap but correctly functioning sunglasses in Boots. How much do you think your Chinese rip-off merchant/ebayer/local market trader cares about what they are selling?
Your choice.
Vin