are you aware of respectacles? you might luck out and they'll have your prescription. the first search doesn't let you refine by bifocals but you can later on. they do truly free used glasses for people in need, and the entire "application" is simply affirming that you are in need. our library does a donation drive for them once a year, and i've helped multiple patrons get glasses through them. recommend!

http://respectacle.org/search?v=2