MB exteded the airbag life to 15 years. There are several threads in the archives on this, including:
What exactly expires w/an airbag?
Air bag replacement???
190E Air Bag Replacement
I plan on replacing the seatbelts rather than the air bag. The belts have a daily use and exposure of the nylon to UV, dust, and air pollution, and are the primary safety system (after driving skills, tires, brakes, and suspension, that is).
Maybe Phil at Fastlane can tell you the price of a new cover for the bags.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E