Nah, Sarah's not solely about the money. She just still seems serious about not wanting a relationship. My guess is she will still go back to ONS and bootycalls if she hears the the restaurant is definitely closed.
I feel like the Mel and Sarah difference is what's happening in the Other's route. Or gearing up for Season 4.
Those two were pretty much the embodiment of the route. Or at least their persona. Cute boy, good sex, have fun, party animal.
Then we learn Mel has some substance, and Sarah is still the party goer/keep everything loose. Even with Sarah's conversation with Ashley, about "scoring someone better", she's clearly an opportunist and not interested in relationships in a personal or serious capacity.
And I think that's how it's going to be with Others. Upgrade to serious relationship (Quinn, Riona, Zoey, Nicole/Lily/Nora, etc., monogamous or polygamous), or stay on the Other's route entirely.