I have also heard that in addition to Plan B or Next Choice not being intended for use as a normal contraceptive, it can be expensive. I've heard it can be $50. While I have never used it personally, I would think that it would be easier, and make more sense to practice safe sex.
Here are a couple articles about that:
Looking for the Safest Sex, and Help! The Condom Broke During Sex: How to Prevent "Wardrobe Malfunctions".
Here also is a good article: Am I Pregnant? Myths and Facts About Sex