At a minimum I would say $100 a day.
We are always way above this though.
Some tips would be to take a look at some of the menus or use the WDW app or
MDE and go through the mobile order process just don’t submit lol.
Also a good way to budget is to visit the gift card section of this site to find deals there. You can add a $25 card on your weekly trip to the grocery store and before you realize you have a good sum for your trip. You can combine the cards at disneygiftcard.com so you only have to take one down.