Why would you ever pay more than the $14/day rate?
As long as you have a gogo account already (not sure how it works otherwise, but is tracked through email)
- Open browser
- go to USAirways.com
- Search for gogo
- buy a pass for $14
- use the pass
This at least works on Delta flights where the pass is purchased completely through Delta. For US it looks like it kicks you to the gogo site, but I would assume you can get to that without paying as well.
I've usually just done the 30 minute mobile pass on US Airways since my flights are short. Just spoof the user agent of a mobile device on your laptop browser and you can get the mobile rates.