Montgomery+Donovan would probably cost Yorke/Drohan/Murphy…need to poke around on BTV. Might be light.
I imagine letting Yorke go would be more palatable if Donovan/Gorman were coming back considering the presence of Story and Mayer.
St Louis, reportedly, has it's eye's set on pitching. Just for what it's worth, on BTV a deal of Donovan and Flaherty for Yorke, Winckowski, Drohan, Mata and Paulino checks out as a minor overpay in favor of the Red Sox. You'd probably be looking at something around that in terms of value to get Donovan and a pitcher (Montgomery is, at least on BTV, worth a good bit more than Flaherty).
One thing in favor of Edman (other than that he'd be a lot cheaper, because he's not nearly as good) is that he is a switch hitter. Considerably better against LHP than RHP, but for his career his OPS splits are .822 and .695, so even against his weakest side, he's still basically Arroyo with the bat (and much better on his strong side) at least for career averages.
I'd have to assume it would be very costly (as others have mentioned) to land either Donvoan or Gorman, but I'd be pretty on board with acquiring any one of those three.
@BaseballJones - figure maybe they tack a year on to Turner (seems to like it here) but then you don't have a DH. Then when it comes to it, you can always move Donvoan to an OF spot, or cycle guys in at DH to keep everyone fresh among Donovan, Yoshida, Devers, Story and Casas, mixing and matching around whoever is the better defensive SS at the time of Mayer or Story.