In my opinion, this would be a good move to make for the Cardinals. Even though the starting pitching was bad this year, Montgomery was a bright spot until he was traded.
With that being said, he's somebody that could very well be within the Cardinals' price range. Pitching won't come cheap, and Montgomery is a client of Boras. That could potentially raise the asking price to a point that the Cardinals may not want to reach.
But he's durable and somebody you can plug right into the middle of your rotation next year. It certainly makes sense on paper. We'll just have to see what his market looks like this winter.