Dizzy Amusement Park is open from 8:00 am till midnight every day of the year. Dizzy charges its patrons a daily entrance fee of $30 per person which gives them unlimited access to all of the park's 35 rides.

Dizzy gives out a free T-shirt to every 100th customer entering the park. The cost of this T-shirt would best be described as a:

fixed cost mixed cost step-variable cost true variable cost