I saw this just now on Armslist: For Trade: marlin 336cb 38-55. He wants to trade for a Marlin 336cb 30-30. He's in South Dakota which is a bit far for me to drive but if anyone has a 30-30 kicking around out there it might be worth checking out.
You can get an idea watching Gunbroker. The 30-30's do not come up for sale as often. Higher price due to lower production numbers. I'll let you know what the market is after the Wanenmacher Arms Show in April.
Okay, just got home from the Wanenmacher Arms Show. I walked the entire upper level of the show and saw exactly ZERO 336cb's. Probably 2500 tables or more on the upper level of the show. Didn't have time to see the entire 1500+ tables on the lower level but struck out there too. 1893's ran from $900 up. One used 1895cb for $1150, one used 44 mag Cowboy for $850, and one NIB 41 Cowboy Carbine LTD for $1300. To sum it up, I saw three Marlin Cowboys at the worlds largest arms show.