I usually go to Costco - no membership needed for the prescription visit ($79 out of pocket for lens prescription, $99 for lens+contact prescription).

You DO need to be a Costco member to buy frames there though. They range from $60-$200 for a pair.

(I actually called them about their prices yesterday).

I usually buy my frames from Firmoo, but there are other online suppliers that sell inexpensive prescription glasses too.