All streaming services are indeed blocked, as well as VPN connections, and there's also a limited number of people on board who can use it at once (usually 10, but it varies). The Wi-Fi comes from a cellular connection to the ground over LTE, so everybody on the plane is essentially sharing a cell phone's worth of bandwidth. On a flight from LAX to DCA the Monday after Thanksgiving, I was blocked from using Wi-Fi for the whole flight as congress and their staffers were on board and jumped on it first thing, stayed on and locked everybody else out. That was a VERY boring flight ...
Depending on flight length, cost varies from $10 up to about $25. For that price, you can get some in-flight entertainment that you can use yourself - that's half way to a decent cheap tablet, even! (The HP Stream 7 is a $100 full Windows tablet, for instance).