The sky diving gives you more utility that whatever else you might spend $200/$20 on. Money is mere a neutral medium of exchange. You might rather express it in

The sky diving gives you more utility that whatever else you might spend $200/$20 on. Money is mere a neutral medium of exchange. You might rather express it in terms of liking sky diving more than your ability to pay rent for x period, or eating out a number of times, or buying books for your next semester or any number of other things that might cost $200, and that you then can't do if you spend the $200 on sky diving.