Masterson is a good option, but there many others. Among the free agents worth considering, there are Hammel, Volquez, Peavy, Brett Anderson, Morrow and old friend Aaron Harang. As the game of musical chairs winds down, one or two are likely to be left without a seat and their price will start to drop.
There is also the trade market. Teams that could be looking to move starting pitching include Toronto, Tampa, Oakland, the Mets, the Cubs (remember Edwin Jackson), the Reds.
It will not be hard to find a starting pitcher. And the price is going to drop. Hart needs to be patient on this one.
The reason I point Masterson out (and think we should pounce early) is that he has by far the most upside and could deliver the highest return if we tried to spin him off before the trade deadline market really heats up late (kinda like Theo and Jed did with Samardzija) to get the best return - especially if the receiving team wants to extend him since they won't get a comp pick.
I definitely won't disagree that we should be able to get a competent guy to fill out the rotation if Minor's not moved or they prefer to keep Hale in the pen (or as depth).