We need help for a group fare?

My Model United Nations class is going to San Francisco for a conference. We are here in Tucson, Arizona but are willing to fly out of Phoenix. We have 24 students and 3 chaperons. The president of the class proposed that we leave March 3rd, giving us no time to sightsee at all. I proposed leaving March 2nd, which will cost more money but give us more time to sightsee. Our teacher already screwed us out of 2 other trips (UCLA and Georgetown) but our money carried over, so we have about $10,000 to $12,000 in the account. What is the easiest AND cheapest way to get there with 27 people from Phoenix to San Francisco? Can someone help me out here? Because the president got a deal of 27 seats for $3800, I feel like I need to find something withing $4300 for 27 seats. Can someone help me?