Great stuff Giles. My mom has the same exact fire extiguisher and she bought it about 3 years ago for $50. Here's has alot of putina on it and the hose is frayed a little.
I feel that one should be worth about $100 or so...
I didn't think those extinguishers were that common, I figured most got scrapped for the copper. I remember seeing those in my parents apartment building in the early '70's. They got replaced around then, to meet fire codes.
I'd gladly pay $100. for it, not sure how much more, I'd be willing to go.