I have had nothing but good luck with getting just about anything in cancun. I got percodan in the first phaarmacy I walked into in playa del carmen. As for the price; the pils are actualy just slightly cheaper than a U.S. pharma would charge so dont expect any mindblowing deals. Most of the cost is for the script you have to get from the doctor. After telling the doctor what you want and getting the script, then buying the drugs at the pharma you generaly have paid as much or in some cases slightly more than if you had got the same meds off the streets in the U.S.
Anyway I guess what I am trying to say is that mexico is easy and quick for getting the drugs you want and most people I know will pay whatever it takes to have a pocket full of happyness when partying south of the border