Probably worth less than you are hoping for.
8 3/8" are hard to sell. A 6", even though much more common,
will usually bring more money. 657s are hard for shops to sell.
Here on the Forum, you have a much better chance.
I have 2 57s and a 657 in 8 3/8" but I am a 41 enthusiast
The 657 was bought at a gun show several years back with a
2x Leopold scope and a leather shoulder holster. Fellow was
asking $800, I offered $550 and walked out with it.
My LGS had a blue 57 in the case for about 6 months this year.
Asking $700. Super clean, barely a turn ring. Since I had one,
unless it was very reasonable, there was no need to buy it. I
walked out with it a couple of months ago for $475. Made the
offer every time I went in the shop and finally they took it.