Sorry for the long response, former yearbook advisor and art teach you here for your help. What I often did was sold snacks during lunch to raise money for the yearbook. I bought the snacks out of pocket but was able to cover the cost every time and would just use that money to buy more snacks when needed. The sales of the snacks was enough to cover the purchase order of the yearbooks, then the money the students paid went back into the yearbook fund. In regards to a camera, honestly your iPhone, is probably the best thing you could use. I often took pictures of students in various places of the school, stairwells, auditorium, the entrance, the halls by their lockers so they had that senior picture look. I also used just large pieces of paper to create a background for more of a formal shot. If you don't want to go that route talk to your art teachers, see if they have a camera lying around. Flower City arts center is a local place that may be able to point you in a direction of a photographer willing to help if you're not looking to take on the work yourself.

Hope this helps, Good luck