Wal-Mart has started a new prescription drug plan that is going to retool the entire industry. The company is now taking 291 popularly-prescribed generic medicines and charging just $4 a pop for them. That’s right. Just four dollars. Wal-Mart is going to start this in Tampa and, if it works, Wal-Mart will roll it out around the country in 2007. That goes for Sam’s Club stores, too. As it is now, generic drugs are sold at pharmacies at very high prices. They may not seem expensive but the mark-up is huge. So, Wal-Mart is taking a page out of the playbook of Costco, which only marks up generic prescriptions 14 percent. That is a lot less than most pharmacies. Wal-Mart’s move is going to blow the market wide open.