Not currently cataloged.
Unknown caliber. Contact Ruger
Yes.
Ruger's web site has extensive sn data.
If the ruger site comes back up, you can check there sn database
100-400
400 USD or so
Go to Ruger's web site to find out.
Just bought a Ruger Mark II .257 Roberts paid $549.00
100-500 or so
100-500 usd
100-450