I travel a lot and I always feel ripped off by airlines.

And I don't trust all those cheap-travelling-portals that claim to do price comparisons between all airlines.

I would love to have an app that visits multiple airline sites every hour and gets the cheapest available price for a given itinerary.

The results should be saved into a database so that one can generate nice charts upon it and discover the magic mysterious patterns airlines use for their pricing (I still believe someone just rolls the dice).  

Email alerts when prices drop below a given threshold would be nice to have as well.

This is a tricky beast because a) this is probably illegal and b) almost all airline websites have set up all kinds of hurdles to piss off robots and screen scrapers such as

• flash plugins
• deferred loading of pages via ajax
• needing cookies
• having session information encrypted in the response, needing it to go on to the next site (a simple post request to the next URL will not work) 
• input fields that rely on javascript being enabled
• html code that is not valid (madness !!!)

During the last few months headless browsers where on the rise in the Python and also in the Node.js community. I haven't checked all of them but I have some on the radar. Also more and more airlines offer mobile versions of their sites that cannot implement many of the hurdles because most mobile browsers wouldn't be able to cope with it. This might be another possible attack vector.

I'm not sure about the legal issues. If anyone is interested in hacking on this, we should probably first do some research and discuss those :)

I have done this some months ago but I gave up because in the end I failed hacking Singapore Airlines because of their extensive use of JavaScript. It; s a cool project for keeping several people busy. We would have to implement one framework app and each airline should go into a module that can be registered with the main app. The main app will send information about the flights to monitor to all modules and the modules will return the cheapest price. The work that needs to be done for each modules differs a lot since all airline websites must be hacked in individual ways.