And 22 Remington Special, which is how the 12 shoud be marked, I think (mine is). Can't shoot a regular 22 LR in it but you can shoot the 22 WRF ammo in a 22 Mag, although I don't know why anyone would go out of their way to do so.
The 12's are pretty collectible. Don't believe me, check out gunbroker or such to see what they bring. That price might not be to far out of line. And if it had a Marbles tang mounted peep sight you can add another $100 or so. Cool old rifles if you want a hundred year old pump 22.
And although ammo was discontinued, it's been more or less regularly available since 1994 or so and isn't any more expensive than 22 mag ammo. Midway, Natchez, Cabelas, etc. typically have it, so somebody must be buying and shooting it.