Football fans shell out hundreds (maybe thousands) a year because they have no choice, vantage points overlooking premiership grounds are few and far between, so its pay to get in or subscribe to Sky TV.
"Spotters" do just that it doesnt have to be at the airport, photographers on the other hand, do have to be near and will pay to do their thing, take Sharjah for instance, I think the last time I did Sharjah it was £40 for the day.