Greetings from the Florida Panhandle
First off, welcome to the Forums. We're glad to have you with us.
Not a bad looking Airstream, but as far as true value goes, it is difficult to say without a lot more information. As has already been said, RV refrigerators are quite expensive, and you already know that you are going to have to do one of those.
You will absolutely need tires at about $100 each. Even if the tires have a lot of tread, they are at least eight years old (probably a lot older) and are therefore dangerous. There is also a very good possibility that this airstream is going to need brakes, and possibly a new axle.
You say that the interior in tattered. You are going to need to spend some money there also.
To determine value, take a look around Ebay and the Forums' Classified and see what similar units are going for. If the one that you are looking at is fairly decent and ready to camp, take its value and deduct what it will cost to put this one in comparable condition.
Good luck in your pursuit of your Airstream.
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2005 Suburban 2500 Quadrasteer (Olivia) & 2011 Silverado 3500 (Fred) with Outfitter Truck Camper (Ethel)