whats it worth

nauti77, I have a 78 SN with almost the exact description. You just described mine to a "T" except that mine is running. i just got mine running, with the help of correct craft fan members,but it had been sitting for many years so I was gonna repair some soft spots in the floor under the front seats. well I soon found out that my stringers where rotted from the front of the motor to the back of the battery box(about 20"). I carried it over to the local marina and talked to the mechanic(who is an excellent inboard mechanic and ski boat restoration "Guru")and he said that it would be next winter before he could get to it. well i didn't want to wait until next year to be on the water so i bought a ski supreme last week to get through the summer until I can get the SN back on the water,which gets back to your initial question he told me that my boat was worth 1500.00 the way it sat with the trailer. He also said it would cost Around 1500.00 to put new stringers and floor back in it.
So I would say that you looking at a 1500.00 dollar boat "give or take a couple of hundred". I have elected to keep mine because it is worth more to me than the 1500.00 dollars. even if i have to put more in it than it is currently worth. I know what I will have once completed and what it will be worth to me.
You may try EBAY, I saw one on there a couple of months ago that souded like ours and it went for about 1300.00 if I remember correctly.