I've never been a huge fan, but given where the Tigers are I wonder if Castellanos doesn't make sense as a target for the brass. With Candelario now on board and only two arbitration seasons left, there likely won't be a better time for them to move him. Since they'll be trying to move Iglesias and Kinsler with no solid replacements for them on the horizon, they might be willing to take Camargo back as a significant piece of a deal for him (in turn allowing us to sell high on Johan in the same deal). If this is what our scouts believe Castellanos is going forward and you can get him for a package like Camargo, Demeritte, and their choice of Touki or Muller you could immediately sit down and talk extension with his people. Start teaching Riley to play LF, and you've at least got your in-house replacements for every offensive position in place.
Even if Dickey did decide to come back, that leaves a lot of money to throw at Joe Smith, Pat Neshek, and Brandon Kintzler types to "fix" the pen on shorter-term deals and maybe Addison Reed for as many as 3 years.