Balloon tours are usually booked by the tour, rather than by the hour. Some companies do offer any hourly rate but require that you notify them in advance where you wish to travel. The pilot will not be allowed to deviate from that itinerary so be sure to be as accurate as possible.
Balloon flights are very popular over the summer months so it is important to book early to avoid missing the date that you wish to take the trip. Some companies only have one or two balloons but you may be able to combine with other couples or families on specific dates. Let the company know if you are willing to share your trip with others.