I'm American living in Finland
Metformin here costs about $8 for 100 500mg tablets.
One time I had an ear infection, I got Amoxicillin for about $40 for 20 tablets! So if one drug is inexpensive, they will just make up for it somewhere else.
I think in some countries, they lower drugs that have a high demand. I believe I heard China has a high population of diabetics, so that could be why it's so cheap there.
Bee