Rotting rodent died in dash panel

I took my car to the shop to investigate a truly atrocious odor emanating from the passenger side of the vehicle. They told me a mouse (or mice) climbed through my car and got behind my dash panel somehow and are now rotting and causing the unpleasant aroma. They estimate $1,050 to take the dash panel out and get it all cleaned up. Is there any other cheaper way I can get rid of this horrid smell? I'm willing to do it myself if I could get proper instructions. Any insight is appreciated.