Actually, I don't really know what the material is in that "X" post is.
There are many types of ball valves, and I really don't know all the types that are used in oilfield operations. So most of what I have posted already is mainly just guesswork.
The most important thing I know for sure is that MVNT is currently machining Inconel balls for some type of ball valve. Inconel is the key in my price guesstimates because of its significantly higher price than ordinary 316 stainless steel.
Disclaimer: Do not rely on my projections or opinions to make a buy or sell decision. Always do your own DD.