Great writeup, there's definitely potential to do something cool, especially if it's possible to get around any tracking and the following price manipulation. I tried installing your demo client, however on running it I got the following error:

  root@kayak:~/kayak-mobile-client# python client.py 
  Departure airport code: LBG
  Destination airport code: HAM
  Departure date (MM/DD/YY): 12/26/14
  Traceback (most recent call last):
    File "client.py", line 56, in <module>
      searchid = json.loads(r.text)["searchid"]
  KeyError: 'searchid'