I have the app that knows where I am located so it gives me prices in my area, but you can use the web site too. Enter your medication, and they give you the price of the medication in your area. Amazing how much difference in price.
Also, if you find it cheaper at Costco or some other pay to enter the store type place, just tell them at the door you are going to the pharmacy because it is illegal to refuse you using their pharmacy. You don't need to be a member to use the pharmacy.