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... :)
I hear you on the time point. Thing is, it's hard to get to that place where you have an offer on the table. Starting over would have a time cost, so over the long term, you might've been able to buy yourself more time with the time you'd already invested.
Of course, that also depends on the amount of the offer.
Have you considered selling it to another entrepreneur to carry on instead of shutting down completely?