It is called business. If you got to 6 non-fast food restaurants on 6 different nights and order a cheeseburger, do you expect to pay the same price at each? Red robin has theirs for 6.99, Applebee's is 7.99, your local greasy spoon only charges 5.99 and so on.

Each track is a different business with different operating costs. Each one charges what they feel is the appropriate entry fee to hopefully break even or turn a profit.

Anyway, It is no different than their regular show. Some track charge more.