Delta.com is free, and sometimes Facebook and/or Google are free as well. On my last Delta flight I could access gmail without ever buying or logging into Gogo. (And yes, it was live gmail, not a local cache -- I sent and received emails in flight.)

Chromebook laptops come with several Gogo access passes.

Gogo is cheaper on a mobile device. You can change your browser's user agent so it appears to Gogo as a smartphone. This flirts with unethical territory but many respectable people are open about doing it (as they would be open with deleting NYTimes.com browser cookies to read more articles for free).

You can also email Gogo after your flight ends, complain that it was slow, and receive a full refund. This is blatantly unethical unless the service was indeed unusable, which it often is, actually.