The Blue Book of Gun Values will give you a ball park. They don't show up often for sale.
50-150 or so
Auction Arms has one on its site.
triplek.com
Old gun catalogs and magazines.
25-100 USD
10-100 usd
25-100 or so
50-100 USD
70
-50-300 usd
100 or so
You need to contact Ruger. You may have a prototype