I once was involved in buying a Canberra PR9 in full working flyable condition from the MoD. Including free delivery to an airfield of our choice, it cost less than £20,000.
A Sea King that has been gutted of the major expensive parts for up to £20K - I don't think so!
No salesman worth his salt will sell you an aircraft, or any capital equipment for that matter, for free. Methinks therefore that the seller will be making a good return on these carcasses.
And, no doubt, you could be charged for lifting it onto your trailer as well.