I just Purchased damaged 02 WRX and front end for it.

I need both front air bags ( Do I need new computer), oem grill, and head lights.

Where can i get these part cheap.

 

You can only get air bags new from a dealer, junkyards are not permitted to sell used airbags. Also if the bags have deployed you must replace the airbag control module inside the car, and probably the sensors as well.
For the other parts you can try junkyards for used parts, and online dealers for new ones. Look in the private and vendor classifieds here and at NASIOC. Grills and headlights are frequently available in good used condition from people who have modified their cars and are selling their original factory parts.