Hi guys,
This is my first time posting in the forum, and I really need your help.

I've got an inexpesive guitar (Epiphone AJ-100), but its the only guitar I have because I dont have the money to buy a nicer one.

About a month ago, I noticed a squeaking sound on a side of the back of the guitar. As I pressed down on the backside, I could feel the wood go down along with the squeaking noise of wood rubbing against each other.
So I got a flashlight, peered into the sound hole and found that the last bracing is unglued to the back at the end where it meets the side-panel.

So here's where I need help:

Is the unglued portion of the brace the cause of the loose back?
If it is, can I just glue the bracing down myself with wood glue? (I can definitely reach it through the sound hole)
If you don't recommend the 'do it yourself' fix, how much do you think it will cost to repair at my local guitar shop. It really doesn't make sense to pay big dollars just to glue down part of the bracing.

I know this is a cheapy guitar, but I play it everyday and take care of it so its something I would like to fix.

Thanks for any help you can give...
Yes, and yes.

Look around and double check, make sure you didnt miss anything else.