Hi Lucy. A rough guide on values that is updated regularly is at Price vs. Condition - Airstream Values
. A big skin patch? A fridge will go north of $1000. For some easy access fridge prices, see campingworld.com (though I wouldn't necessarily buy from them) and search on refrigerator. Look at a 6 cu ft or greater Dometic or Norcold price.
The shower mixing valve is notoriously sensitive to freezing if it was caught unwinterized in the past. That's supposed to be a tough fix, requiring removal of partition walls, the shower module and more. And the owner messed up the shower enclosure to boot? I'd agree with azflycaster -- you could put a long restoration into even these limited problems (not likely the end of the list either). You could easily put a 2-3 thousand into the earliest repairs and still have a tough time selling it for $6100.
Do you know that the air conditioner works? The owner would actually need to have a 30A outlet (or find a local campground?) and turn it on in warm weather. Don't use a 15A-30A adapter for this test.