Re: Jayne Cobb
The movie left me with the impression that Jayne has changed since the series began--that he's buying into the mission now. He's the one who, according to Joss's screenplay "speaks for them all" when Mal calls on them to act in his "I aim to misbehave" speech. Jayne got more than muscles from pumping iron with Shepherd Book: he got righteous, so now he says that "if you can't do something smart, do something right."
I admit that Jayne washes down that righteous declaration with a swig of what might be alcohol, which could indicate the need to steel himself, but he seems sincere. And he passes the jug to Simon, his erstwhile main critic on the ship, which underscores the feeling that Jayne's seeing himself as part of the group.
And we know he's capable of great love for his biological family (that silly hat he wore so proudly!), so I can believe that he's capable of feeling a kind of love for the Serenity crew.
But Ray's question makes me wonder: what is Jayne's price?
Did he ever want money for money's sake? Or did he just want money for the guns and shelter and womanly companionship that money could buy?
If money was just a means to comfort, then maybe he's getting enough guns and shelter and companionship (at least in "Heart of Gold") to not feel so tempted to betray Mal?
Then again, plot twists involving gray areas of morality are Joss's thing.