[annnnd]

Hmmm. If it's about users, then why shutter the service they depend on? I am sure you have throught about this a lot and are probably tired of investing more time and energy in this project, but if you have hundreds of thousands of users, you have a huge opportunity on your hands.

How about:

1) start building your own set of data to complement the bought data. Every time there is an inaccuracy, approach the airline company and start using their data directly. Later on, you can even become one of the companies who provide data to others. When there is a problem ("the data companies are not doing their job") there is an opportunity.

2) change the pricing model to charge big users more. They should be your bread and butter, because they get paid to use your app. You are just a small additional cost to them. You can even lower the initial price tag and charge more for enterprise usage... Since you are better than others (see 1.) the enterprise users will be happy to pay more.

3) failing that, sell to an entrepreneur who will continue. I am sure there are many interested persons and your users would be better served if someone picked up where you left off. Hell, I am interested... :)