USA = cheap glasses! Def!
However, keep an eye on Boots. They often have their £30 glasses on offer as a BOGOF (buy one get one free) making them £15 a pair and they're designer styles, metal with bendy-back hinges and all. You have to look through a load of chaff though in order to find the polarised ones.
Short of that there's some in tackle shops under the name of Eye Level. Pretty good I hear and keenly priced.