I saw one of the S5S's that was new in the box go for about $160 a few years ago, and than a couple used ones without a box not sell for far less. You see more of the very similar S6S's for the Sporters and I have seen several of them sell in the $50 to $75 range. Neither are common sights but they do not seem to be popular or command very high prices, probably due to them mounting on the wood and other quality receiver mounted sights being sometimes available. There currently are a couple S6S's on ebay that have really high staring prices and have been getting relisted for a very long time (and will probably never sell unless there is a drastic price drop).

I bought a S6S a few years ago for about $50, but I had a 1922 Sporter that already had the holes in the wood for mounting it, I would have not have bought one to put on a gun without the holes already being there (and I would shy away from a rifle with the holes unless the price was very reasonable).