The MADE IN USA together with the magnas makes it a likely 1946 to 1948 vintage, most probably a long-action S-prefix M&P although it could be a low C-prefix and/or have the short action already.

These aren‘t rare, but at something around 200,000 or so made, not as common as later Pre-10s or Model 10s. For condition, I don‘t do percentages, but for 500, it would have to be in very good shape. But the price is not out of bounds if you like the gun