Except quality starting pitchers with team control always command a huge premium at the deadline and the Yankees are going to be at the very bottom of the list of teams we want to trade him to, so unless absolutely nobody else is interested (unlikely) the Yankees are going to have to overpay significantly. I would have thought that someone like Bauer is a more likely target for you.
Bauer has been my top "realistic" target all along. But there are next to zero rumors linking him and the Yankees. I don't know if Cleveland will be sellers. This is probably a wash year, but they're still a good team, so maybe they just hang on to him.
Stroman was at the bottom of my want list, not because I don't like him, but like you said, he'd command an additional premium, plus if the Yankees trade a guy like Frazier to Toronto, he's the kind of guy who will use it as motivation to torment them for years.
Right now, my list is:
Scherzer (Who isn't going anywhere)
Bauer (I don't think he is either)
Stroman (I'm scared of what it will take to do it)
MadBum (Who knows how he'd pitch here and if he'd still be the same October guy)
Boyd (I'm not particularly fond of him)