I would have to say I'm surprized it would be worth that much when the artist is unknown??
How do you go about selling this type of item, and getting anywhere near that kind of money?
There are a wide variety of ways to sell as I am sure you realize. Auction provides rapid return without seller protection. Galleries such as Skinners, Bonhams, Kaminski, Butterfield's have all shown success with surrealism. Consignment to the proper fine art gallery is also an option. Unfortunately commissions are usually 40-50%. Ultimately the definition of value is the final price agreed upon by a buyer and a seller. Here a a few that might help.