Hi Vanessa!
Thank you so much for the direct question. That is awesome that you and your classmates are traveling to Walt Disney World, you will love every minute of your experience!
Not knowing your full plans, I will assume that most of your meals will be counter service meals. Meals bought at counter services do not require an advanced dining reservation, and allow you to have your meal at your leisure. There are different meals to choose from, so you will not have to eat the same thing every day for every meal. One location that comes to mind as an example:
Everything POP Shopping & Dining at Disney's Pop Century Resort.
I would allocate about $40 for lunch and dinner, per day, with an additional $20 set aside for souvenirs. The good thing is if you have monies left over from your allocated Per Diem, you can use those monies to enjoy additional souvenirs.
I would like to make one suggestion that could be a true cost saver, and involves a one-time cost of $15.49: The Resort Refillable Mug which allows you to have free unlimited refills of beverages throughout your stay until you check out. The beverage station offers soft drinks, iced tea, hot tea, coffee, and hot chocolate. I think that you will find the mug to be fun and convenient.
Please let me know if you have additional questions and have a magical time!
Raquel