If Price is so high on the cubs which again he seems to be, why give up anything unless you literally view him as the last piece to a WS team? You could in theory just sign him next offseason for probably just money since as you're saying he may get traded which voids the QO.
Ultimately, the problem the cubs have is they need offense but they really don't have the places to play offense. The entire infield is full of future players for the cubs unless you're trading out Castro for Baez/Alcantara/whomever. RF should be Soler's. That leaves CF, LF, and C. Outside of Rizzo and Bryant, Cogs and Montero have been the cubs two best hitters. And as for Fowler in CF I've more than supported my argument on keeping him but even if you change him out who has enough impact to really change the offense? Carlos Gomez is arguably the most talented CF available and he's hitting .268/.329/.440 with 8 hr's and 7 SB. Fowler is hitting .235/.321/.368 with 8 HRs and 13 SB. So, clearly Gomez isn't a substantial upgrade here at least not enough to push the cubs over the hump offensively. Like it or not, the cubs are going to have to get more out of their young players and especially Castro if they are going to contend. Their pitching has been some of the best in the league.