They even made it to Korea. Price? when they first came on the market, they were $25. Have no idea what they are going for these days. Selling it, if you must would be a good idea to sell the rifle with it.
I bought one set many years ago from S&S firearms just to get the grenade launching sight with it. If you noticed those two little holes halfway up each side of the mid barrel band, thats what the grenade sight pivots on.