I found these on eBay Motors:
1940 Airstream Mullins Antique Camper, Street Rod Trailer, Rare 40's Vintage! Item number: 270228694655 Current high bid: US $647.37 (Reserve not met) End time: Apr-27-08 18:45:00 PDT (1 day 18 hours) Item location: Knoxville, Tennessee, United States
AND the other one may be out of your $ range, but it is closest to your description:
1958 Airstream Traveler 18 Footer
1958 18' Airstream Traveler Item number: 270231307378 Current bid: US $2,550.00 (reserve not met) End time: May-03-08 07:00:57 PDT (7 days 6 hours) Item location: Bat Cave, North Carolina, United States
Good Luck!!