What is the difference between bread dough and pizza dough?
You can use frozen bread dough, just fine.  You'll often see it suggested in recipes.  Pizza dough sometimes is made from higher gluten flour, or goes through a slower rise to make it more chewey and stretchy, but bread dough is definitely a major upgrade over pre-cooked crusts.

Another option is call around to some local pizza shops (national chains usually won't do this) - many of them will sell their dough for about $1 a ball (good for about a 14" pizza).