Oh that's a HUGE bag of worms. Not only do we get vastly overcharged in the US for our prescription drugs (as compared to the rest of the world) but our insurance is all different for different people on different plans... and then larger pharmacies can afford to offer discounts so sometimes they are cheaper. But then on specialized stuff sometimes the smaller pharmacy may be better (they may pay closer attention to the work, etc.) and you may get better pricing to. Welcome to the free market in the USA. Its insane.