I have a small collection of Kasiner extruded aluminum cars and one Rail Chief Magnesuim (I think) car. The Kasiners are quite similar to the OK Herkimer Cars.
Yes, I believe that you could get $15 or so for unassembled OK Herkimer kits. Best of luck on selling them. I sell items on ebay and usually I get about what I think things are worth. I intend to list the Kasiner cars soon.