If you have to wear them constantly, like I do, remember to wipe them down with a gentle soap periodically. The spaces between the frames and the lenses will collect gunk that makes you think something is in your eyes and drive you crazy.

@paris mentioned one online retailer already but to give you another option: I've been using Zenni for my prescriptions for a few years now and have been happy with them.

Sometimes a vendor or optometrist isn't contracted with your vision plan, but you can often submit for reimbursement; some health insurances (since eye health isn't health, somehow) will also allow you to submit for reimbursement so check your policies, if applicable.

I tend to order two non-tinted pairs and a pair of prescription sunglasses when my Rx changes noticeably - one pair is made of safety polycarbonate (shatter/puncture resistant) and the other is more standard, but it's nice to have options to choose from. As you go through them, please make sure to donate your old prescriptions! I've sent most of mine to the Peninsula Special Interest Lions Club in CA but there are a number of charities that will send your old lenses and frames to people who need them