For an individual photo mission, the airplane generally has a higher operating cost than a drone, but lower than a helicopter. But, with a 5-hour flight time and 150mph flight speed, multiple photo missions can be bundled together, keeping costs down. Even though it may be more expensive to operate, more photo missions can be done in less time, making it a very affordable platform.
For videos, the airplane is much more limited than both helicopter and drone platforms. It allows for only circling and panning footage. While this may not be desirable for an exclusively video photo mission, it can be inexpensively added-on to any photo mission.