I want to have a block party for the fourth. What kind of food can I serve that is cheap? I'm having hotdogs.?

and chips with salsa and kegs. I want to serve inexpensive plentiful food. I don't know how many people are going to show up. I would say at least thirty or so. Maybe more. My needy neighbors with unending appetites. My sister has a Costco/Sam's club card. Should I go with that or with Sav-a-lot??