A restaurant serves between 100 and 200 people every evening. Each customer buys either the 'Meal of the Day' at $20 or the 'Gourmet Meal' at $40. No more than 25% of the customers on any evening buy the 'Gourmet Meal'. All drinks cost $5, and everybody has at least one drink, but nobody ever has more than four. On the basis of this information, what is the difference between the smallest total amount and the largest total amount customers might spend in any evening?