Hello pilato. Welcome to the Forums!
What you are asking would require a significant dedication of personal and private research on your part -- if it is attainable at all. By this I mean a unit with worthy running gear, wheels, tires and floor. Pre-1974 wouldn't have a gray tank. And $11K is below the current street value
of a usable Airstream of this length and vintage.
Sub-20' Airstreams have been in high demand for a long time. A Pacer? 13 panel or 1950
Airstreams are very strongly sought after -- and tend to be huge gluttons for significant restoration dollars. I'd suspect you're looking at $30-40K or more if you pay somebody like GSM Vehicles
to make an as-found unit usable -- the better part of buying new. Whether doing it yourself or paying to have it done, you could be looking at as much as 12-24 months of serious dedicated attention.
I'd suggest getting to one of our member-sponsored rallies
if you want to sound out knowledgeable and actual users about what it takes.
What questions can we answer for you?