Asda Opticians currently have an offer on where a complete set of glasses with frames costs just £50 or £90 for two pairs.
This includes all frames, including designer but what makes this a really good deal is that if your prescription requires it, high index (thin and light) lenses are included in the price (Normally high index lens on their own cost more than this).
I managed to get two complete glasses with 1.74 high index lens (thinnest plastic available) for just £90!!
Tried to search if this was a repost - apologies if it is.