There are tons of used Airstreams for sale, and the bigger ones, 30 feet and up are less sought after than the small ones so there are many bargains available.
I personally feel that $9000 is high for a '77 unless it's had a major renovation. Many 70's units have frame separation and the axles are starting to go, which are both expensive to fix. Another BIG issue would be the appliances which may need replacement - water heater, furnace, refrigerator. Again expensive. Last could be water damage and floor rot. Read "full monte" threads here!
There's a 1996 31 Classic in Virginia Beach for sale at $19,900. Now that is a reality check.
Before you do anything else, think! Go look at the CLASSIFIEDS here. Go on Ebay and look at the current and past auctions to get an idea of current prices, check Craigslist as there are many hidden gems there.
Last ask for a volunteer inspector from this list to look at one you "fell in love with". Failing that PAY for a professional to inspect it before you buy. I'm one of those "Airstream Millionaires"
but $9000 is a lot to spend impulsively.