If you only have money to buy one item (tablet or projector) I would opt for the projector. It can be paired with a computer or laptop an will certainly allow everyone to see. You can store it on a cart and only get it out as needed. If you project onto a whiteboard, you can have the illusion of an interactive whiteboard and “draw” on your images or annotate music. I think a projector would be a better use of the money.
I have a teacher ipad that I use everyday, but not for classroom activities. I use it as a remote control for my laptop and mostly for creating lessons in Educreations or MadLip.