CVS Pharmacy must depend upon prescription drug sales to remain in business, but Wal-Mart doesn't need to add a huge markup to the medications they sell.  The local temperature in the medicine producing country is one and also the other country might be another, and the avian temperature may be the other.  Make sure you take time to ask about a more affordable version so they will look into the list.  
http://guides.womenwin.org/node/104909