Replacing a rear quarter panel is a whole 'nother thing from doing a door.

It's a large amount of welding, few nuts and bolts, if any.

Can you take the car to a nearby body shop? One that does known good work Volvo or not. Get a quote and ask a ton of questions. If you can cut the cost by providing the panel, get an idea of how much of the panel they would need.

The part that forms the rear of the door opening is not easy. They will tell you if that part must be worked on or not.

Then there's the welds where the panel joins the trunk opening and the panel across the rear, and the one at the roof above the rear window.

Good Luck,

Bob

:>)