Welcome. Never heard of a M85 with any kind of "S" in the model. My guess is sloppy handwriting but if you can get a picture of the label, host it elsewhere and link to it here we can confirm that or add to our knowledge.
The earliest M85's were hollow bodies. Circa 1972 or 73 they were re-imagined as a solid body instrument so if your date is 1974 then it should be a solid body and probably looks a lot like (LTG member) guildsofgrot's below.
To the extent that you can compare a solid M85 II with Guild humbuckers to a Guild JS II with humbuckers, I would say that the tone is distinctive, good for some styles but not all. But my opinion is definitely colored by a personal preference for vintage Bisonics.
I have not been following the market. When searching there are three different price ranges. The cheapest will be the Newark Street M85's which are hollow and made within the past few years. Next will be the M85 solid (and I don't recall whether it is solid or chambered but the difference does not matter for this post) which will be circa 1971 through the 1970's. I recall prices from $1500 to $3000 depending upon condition and whether the seller is trying to invoke Sheryl Crow to get a higher price. Finally there are the hollow bodies which predate 1971. Those go for $2500 to $3500 and sometimes higher. It helps to know what you are looking at because sellers who did not do enough research have priced 21st century M85s as if they were vintage and vintage solids as if they were vintage hollows. (note this is a sweeping generalization and I can think of several specific instruments that are exceptions but this covers 80-90% of the market).
My intuition says that a price of $1000 or lower, with case, is either a screaming hot deal or VG condition does not mean what we think it does and there is probably a major repair. Upwards of $2000 and you are either getting outstanding condition or are a committed Sheryl Crow fan.