I'm a great fan of the cheaper glasses with interchangeable lenses. The ones I have are called Body Specs and I don't know if they're still available or not, but they're excellent and low-priced. There is no way I would ride without protective glasses. But there's also no way I would pay the exorbitant sums wanted for the big brand names.

However, if you need corrective lenses in those glasses, it may be necessary to pay the extra. Luckily I only really need glasses for reading.