1879-S Morgan Silver Dollar

I think you're right on it. This Morgan could be MS or AU depending on luster and how the toning is distributed - hard to say for sure from photos. I think it is probably MS in the 63-64 range. Going rate for this coin in these MS grades is about $80-100. The 1879-S R79 is usually very well struck and commonly found in MS.

Edit: regarding variety - the 79S r79 is notoriously hard to attribute. I usually don't even try to do it.