I think these things change on a moment's notice. I never really thought we were far and away the front runners for him especially so far away from the trading deadline. It all depends on the extension. If you sign Buehrle for an extension then the chips you are willing to trade away become a lot more impressive. If you're only getting a three month rental for Buehrle, the offer should start with Jed Lowrie and not advance much past that (maybe Lowrie/Murphy).
But if you can sign the guy for a multi year extension I can definitely see parting with Michael Bowden, Jon Lester, or even Jacoby Ellsbury. If the FO thinks Crisp is turning into the player he was in Cleveland, how much better is Ellsbury going to be? The guy is not untouchable IMO, the only prospect that is untouchable right now is Buchholz. Ellsbury is not in his league, IMO.
Another idea, is it possible that Sox are trying to acquire Buehrle to flip him to the Braves for Salty? The Braves don't have the prospects needed to get Buehrle, and if they could they jump right back into the NL East chase and possibly become one of the favorites in the NL. A 123 of Smoltz/Hudson/Buehrle is pretty good, and it probably gives them the best rotation in the NL outside of San Diego. If the Sox can somehow get Salty for a package of say Ellsbury/Bowden/Lowrie, is that then worth it?