Is this too much rust?

2018 Honda Fit 82000 miles $10.5k I live in northern NY

Looks like previous owner hit something and cracked right behind the backseat door. They attempted to sand it down and paint over it, but it didn’t seem to work out as it looks like it’s bubbling.

There is no rust on the frame of the car which is good. The dealership told me it would probably run me 500-600 to fix. They would also take another $250 off of the price.

What do you guys think? They say it’s mainly cosmetic, but I’m skeptical of that. If I got it, I would want to get to the root of the rust, but I just don’t know if it is worth it. I am confident this car would last a long time. It’s just that damn rust …