How to access the supporter for the striker on the drivers side door?

I have 2002 Toyota echo the striker pad on the drivers side fell off so I cannot close my door. The part it attaches to has either fallen into the body of the car on the left rear side or disappeared totally. Two questions what is that part called. If I have to take the car apart how do I get into the body of the car where the striker plate is attached. Is there a cheaper way to fix this. I got an auto body shop quote for over $400.00 because they have take the car apart. I would also love to see a picture of the frame of the 2002 Toyota echo so I can imagine what they have to take off. I cannot see why they could not drill a whole into the side of the door and retrieve the plate or whatever the striker attaches to. The car is old has high mileage and was really wanting to drive it till the fall.