I have good news and bad news. You can find Mustangs under $5000, and you can find restored ones, but you can't have both. A fully restored '67 will be 10 grand plus. You can buy a fixer-upper in your range though. You could check out some online sites like auto trader.com or even ebay motors for cars located in your area...but my advice is see the car physically first. I'd also recommend searching your phone book for dealers in older vintage vehicles.
Never buy a vehicle like this sight unseen unless you can afford lots of repair and/or know the car's characteristics REALLY well.