High Noon: Back-Up Glasses

I need to get a pair of back-up glasses to hold me over until my insurance kicks in (August) for a new pair of frames and glasses. As some of you know, I lost my regular glasses after covering the North Idaho College trustee debates in Post Falls City Hall last fall. I believe now that someone walked off with them. My Eye Doctor told me that theft of glasses, for various reasons, is relatively common. I don’t need glasses to read or write or even watch TV. I need them to drive. So I’ve been using an old pair since October. However, I wouldn’t mind another decent pair in case I lose the ones I have, too. I’ve gotten the prescription from my Eye Doctor. (SR file photo)

Question: Where should I go for a relatively cheap back-up pair of glasses?