It will depend on what or where you plan to eat, if you are going to be doing counter service plan on $10 - $15 per person per meal. If you are going to be eating at table service either in the parks or DTD plan $20 - $25 per person per meal, more if you drink alcohol.
I would plan on about $125 per day, assuming 2 meals at counter service and one at a table service and one snack per day. There are ways to cut down this cost, eating off site, sharing meals, eating breakfast in your room (muffins, pastrys etc you bring with your or buy at local market)