Translation:Come on, let's go.
It doesn' mean "now", it means like, well as in "ok moving on now", it seems like more of a conversation part rather than a sentence you'll find written down.
It's true that it is the same meaning in english, but the point is so you'll distinct between "now" as in time, than "well then"
じゃ is a contraction of では, oftentimes used as an expression that you are reaching a conclusion, very similar to how you would use "well then" in english.. and さあ is an expression used in order to make the conversation move forward, this is often more forceful than じゃ, which also depends on the tone of context. You could translate さー as "ok now", "come on", "ok let's not dwell on it and move forward".
さあ doesn't necessarily mean "Come on". It can be translated differently based on the context. Here we don't have much context.
さあ Conjunction 1. come; come now; come along; go on; hurry up 2. well; who knows; I don't know...; uh; hmm 3. well now; let's see; there we go; all rightsaid when surprised or happy 4. about that; you see