Yea, they are sought after. I have a buddy who has one on his Sears, he says he would rather cut with a mowing deck, he has never been happy with his. I wanted one for cutting the field, but after his complaints, I just stick with the deck.
Prices maybe kind of high, the sickles usually fetch 250-400, those tractors are not worth the balance though. 1 is a 1977 16/6 single Tecumseh, the other looks to be a twin Onan, guy statesit's a 77 also.
There was a 1968 SS12 posted on my local CL, I text'd him for pics. He was asking $1000, tractor, deck, and rear blade. It was in pretty good shape, but still maybe only a $500 package.
I am a cheapskate though!