Vacation in Chicago cannot be called cheap for the average tourist. Plan to spend at least 100 USD per person per day. This does not include accommodation - only transportation costs and food. By the way, fast food in the USA is very cheap.
Here is an approximate list of prices for a vacation in Chicago:
Hearty lunch or business meal — from 25 to 55 USD.
Bread — 3 USD, a bottle of mineral water — 1.5–2 USD, a bottle of beer — from 3 USD.
Ticket for the metro or bus (if purchased from the driver) — 2.50 USD.
Cigarettes — from 17 USD.
Gasoline — 1 USD per liter.
Accommodation — from 35–60 USD (in a hostel). But if you’re planning a trip for two to Chicago, expect to pay from 100 USD per night for the cheapest hotel room.
The most expensive part of a trip to Chicago, according to experienced travelers, is guided tours. Prices start at 100 USD per person. So if you want to save money, make sure to bring maps.
