Leaks oil from the rear valve cover.

We don't get involved with costs here because there's too many variables. In this case what one person considers a good deal, another of us wouldn't touch if it was free.

As a general rule, when someone is trying to sell a car, they're going to fix all the easy and inexpensive things to make the car more attractive to buyers. When they sell a car with problems, it's because it's an expensive fix, it's a difficult fix, or no one has been able to properly diagnose it. GM cars are designed to get them off the assembly lines as quickly and efficiently as possible. That does not include thinking about future serviceability. You'll notice you can't see or touch the rear valve cover so a lot of stuff will have to be disassembled to do the repair. Any repair shop should be able give you an estimate for cost of repairs.

There's plenty of miles on the car already, and if that is rust on the front of the left strut tower, you better look closely at the bottom. The bottom generally rusts out faster than under the hood.