Ames only has a very small airport that has no commercial flights. The nearest airport is the Des Moines International Airport. Ames is approximately 40 miles north of the airport.
The Des Moines International Airport has several options for rental cars available in the terminal including Alamo, Avis, Budget, Dollar, Enterprise, Hertz, National Car Rental, and Thrifty Car Rental.
Executive Express is a shuttle service that provides regular service to Ames and can be booked here: http://www.executiveexpress.biz/. A round trip from Des Moines to Ames and back looks to be about $86.00 for one rider and $116 for 4 riders, so try to coordinate with others to save some money!
Uber looks to be a $35-81 ride one way depending on how many riders.
There are several taxi services that operate in the Des Moines area. Their fare is estimated at $90-95 one way.