Well my headliner is starting to loosen in the back of my car. And I was wondering how expensive it is to have a new headliner put ina 99 a6.?

 

What do you mean the headliner is starting to loosen? Is the fabric falling off of it or is the entire thing loose? It is very expensive to get an entire headliner replaced.
More than likely the rearcenter headliner trim has some broken clips and you can get those from the dealer for about $3 a piece.

 

The fabric is falling in the back part of the headliner

 

If the fabric is seperating from the headliner panel, you will liekly have to repalce the entire panel, or find a qualified upholstery shop to do the repair. Good luck!