Chicago under $25 PP
That really depends on what you want and where you're at.
BTW: the cheapest place I've brought people was to the Tank on Broadway and Argyle. Everybody loved it, everybody was more than full, and it was only about $12/person. It's pretty down and dirty, though.
What did you have in mind.
I, unlike most, like and recommend Cafe Iberico at Chicago and LaSalle. For $50, you can get a pitcher of sangria and four tapas plates or so, which is plenty, since their servings are large. Last week, I had a delicious grilled oyster platter ( four BIG ones with a small rice salad), a coldcut and cheese plate, grilled octopus with fried potato, and scallops with saffron rice, along with sangria, and the bill, plus tax and tip was under $50.
If you are going on Friday or Saturday, get there early or prepare for a LONG wait.