They are available new, and legal to buy in California (not affected by handgun roster, not an AW). Gallery of guns carries them, but is out of stock right now. Guns.com has the stainless 20" in stock for $733 (and I don't know what barrel length you want). That sets an upper limit on what a used one can go for. I would think that a used one would sell for 70-90% of the new price, or roughly around $600 to $700. To all that you have to add the FFL fees and DROS. Buying a used one ends up a little cheaper (the dealer can only charge the $37 PPT fee, not the typical $50-$150 fee to receive a gun), and the used price might be a little higher because of that.
Nice guns by the way. Getting a good large-caliber lever action is on my to-do list.