I just remembered something that might help tho's that are treating there horses with Metformin as I have seen the comments stating that it is not cheep....
Walgreens has a program for tho's that do not have insurance. You join a club and get great deals on some medicines. AND yes they allow you to add you pets! The club cost is 35.00 per year. I looked and you can get Metformin for 5.00 (yes, five dollars), for a 60 count, 500 mg. tablet.
Hope this is helpful.