According to data from Atlantic Information Services, the average co-payment for a “first tier” — the cheapest category — of prescription drug is $10.28. Medical price information website ClearHealthCosts.com has a breakdown of how much several national discount retailers charge for generic drugs. Most let you get from one to three months’ supply of your medicine if it’s one of the qualifying drugs on a pre-set list. Most retailers on the site have between 100 and 400 generics on their list, and costs start as low as $4 (Walmart, Target) or $5 (Kmart). National drug store chains CVS, Rite-Aid and Walgreens have prices in the $9 to $20 range depending on the medication or amount.