|Google has been offering an API for airfare data at https://developers.google.com/qpx-express.|
I just received this email:
"Dear QPX Express API Customer,
After careful consideration, we've decided to shut down the QPX Express API as of April 10, 2018.
How this affects you
After April 10th, you will not be able to access the API and will no longer be charged for this service. Until then, you will be charged a reduced rate of $0.02 per query for any queries beyond the 50 free daily quota.
You don't need to take any action. However, if you are actively using this product you may want to find an alternate solution before April 10, 2018. If you have any questions about these changes, please don't hesitate to contact us at any time.
The QPX Express API team"
More info on the shutdown: https://developers.google.com/qpx-express/faq#EndOfServiceFAQs