Airbags

Where can i buy a driver side seat airbag? not the airbag that pops out at the steering wheels but the one that is build into the seat so when someone hits yoru car from the side it pops out..... we bought a car at an auction and the driver side door is hit and the guy wants to charge us 800 dollars just to fix an airbag...

edited: Its a 2001 LE 3.5