I've seen model 57 listed like others said, anywhere from $600 - 800. But the bottom line is decided by the buyer and the seller. List it at $800 - 900 all day long, but if the buyer isn't paying, you're out of luck.
I was selling a 57 with 8 3/8" barrel, no box, similar condition as yours less than 3 years ago. I started the listing on the internet at $800. I ended up selling for $600 after about a month of listing.