I just got my first fatboy lastweek. Great little razor, I wish the head profile was a bit slimmer but other than that it's amazing! Congrats on your score!
Unless the case is cracked, you can probably bring it back to life with some Meguires PlastX or comprable product used to remove the oxidization on headlights. I've found that buying razors in the wild is kind of like playing poker, I try not to let the seller see how excited I am (easier said than done when I ran across a Double Ring for $3.00).
Talk about a heck of a deal. I need to find these antique swap meet things. They sound like the place to get good deals when it comes to shaving needs.