Glad to hear of your good fortune. There are various published guides to car values, but in the end it is worth what the seller will accept and what they buyer is willing to pay.
The "average" value listed in the NADA guide is $7,000 for a Cobra II or $7,500 for a King Cobra. The low value for a car in fair condition is around $3000, and the high value for a car in pristine condition is around $11,000.