Why is auto rental so expensive at Bush Intercontinental Airport in Houston?

Prices are based on the law of supply and demand. In this case, many people are going to be travelling through an Intercontinental airport, and most of them will likely be renting a car. If you think the prices are high, try finding a discount by booking the rental car with the airline ticket, with a hotel, or through "relationship" discounts, such as particular employers, AARP, AAA and others.