Well, you only have to tip for TS meals - so, looking at the menus for those places you have selected, take the most expensive item, add any extras you might generally order and times it by 18% times the number in your party.
Example:
Entree/drink/dessert cost ($38) + appetizer ($9) + beer ($6) = $53 x 18% = $9.54 x 2 in party = $19.08 ... or round up to $20.
If you just want to do a guesstimate, I'd say $10/per meal per person should be plenty for budgeting purposes. [Note, I did not include the tax ... but I don't believe you tip on tax ... only on the food/drinks.]
Now if you have HDDR, the gratuity is already included unless you order special drinks that might cost extra. Also, some feel you don't need to tip 18% for buffets, so if you are of that school, the tip would be less for buffets.
Hope this helps!