C240 Rear window
 

The drivers side rear rolled down at the push of a button, but appears to be stuck. A little poking and prodding, it looks like the regulator is going up and down (there is a little square piece of plastic rubbing on the glass). Is this an expensive fix? I'm very mechanically inclined, however the in door airbag makes me stop to think I should job this one out.

Thank you for your help, I do not wish to go blindly into a dealership without knowing how bad it is.

KAM.