Like anything else, it depends on two people agreeing on a price. Condition and location are huge factors.
Millions of these were made and they were precious possessions so they were well taken care of. We value the ones that were in our family, but that really doesn't mean much to a buyer. Some of us have enough treadles that we turn them away unless they have some specific desire. Some of us have received them free.
They are big and heavy and hard to move now and won't do fancy stitches that younger folk expect. $50-150 are common asking prices around me. Some go much higher. Check e-bay sold items or chicken entrails or tea leaves.
I don't know the S model, but it was sold by Sears.