I have only had a limited amount of time to review the data so far but it seems that car rental prices were higher than average (it's possible that people rent more expensive cars, for example, to impress during their fund-raising attempts) and that did contribut to pushing the cost up.

It's also a question of what people spend on dinner and entertainment. In some circles a few $200 bottles of wine is standard.

The study is based on actual expenses, so individual habits play heavily in this respect.