Pay them $5 a month till it's paid and never use them again---but before you pay up find out if there is a way to challenge the payment. (contact the company PR/consumer dept. in writing, registered mail) & tell everyone you know not to use them.
Also, be sure you get the generic, ask ahead of time the cost also---the card should take care of future surprises.
I have noticed some on line coupons for meds too. Drug Companies change the cost of drugs on a whim without notice (and it also makes a great deal of difference, even hundreds of dollars, where you get your RX filled)
This makes me so angry. They need to be regulated.