Levermatic: Model 57 is 22LR and Model 57M is 22 Magnum - otherwise look the same. Aluminum or steel receiver? Steel (later 57M) is concave, aluminum (early 57M) is convex. It should be a walnut stock, is there a bullseye? Spacer at the cap may have been removed, or just cracked and fell out, either way it can be replaced. I've seen 2 model 57 (22LR) come up for sales locally in the past 2-3 years and they went for $350-$400 which I thought was high.
I recently picked up a first year (1955) steel receiver, serialized box magazine style Model 56, 22LR without the magazine for $250. I offered $300 if the guy could find the original 7 round factory mag. It goes with my Dad's un-serialized 1955 Model 56. My dad's Model 56, which he bough in a hardware store for $40 in the early 60's is in my possession and is a very accurate rifle. I shot a 237 score for Rifleman with it at an Appleseed and again used it in a Winterseed to shoot the score. It is not generally picky on ammo, some groups better than others, and I actually get the best accuracy out of it with CCI quiet.
For me personally, $575 seems high, but they aren't making them anymore, it a fine rifle and the market is what someone is willing to pay.
Best article of the Levermatics: