Got an '05 Civic EX (or it may even be DX, its automatic, but has manual locks and no cruise control).

The other day I turned it on and the right side audio was out.

I have NO experience messing with car audio/wiring but some people suggested it could be as simple as reconnecting a loose wire. How involved/difficult is it to get in there and check that?

Or am I looking at taking it to a place and them charging me $$?

 

I think there is only one fuse for the stereo, so they all work or don't (if the fuse is the problem)... moving on

Swap the left and right speaker and see if the problem moves with the speaker or stays in the same location. If the problem moves with the speaker, the speaker is to blame. Not likely if both front and rear on the right went out at the same time, but worth a shot I guess. If the problem stays in the same spot, you need to look elsewhere for a solution.

Other causes could be wiring..anywhere in the car (inspect the wires as you unplug the speakers when swapping around), or the head unit's right output is blown. I wouldn't mess with this until you swap though. Get the simple stuff out of the way first before taring into anything else.

Let us know what you find.

 

Start with your balance control. Make sure that you didn't move it to the left.
Are both right side speakers out? Generally if you lose a full side, it is a bad head unit. One speaker shorting out or disconnected will either take them all out, or just that one.
I am assuming this is a stock unit and there is no aftermarket amp involved.