Considering how much "proven" relievers are getting, I'd be looking for failed (or old, injured, etc) starters to add in bulk.
Mike Minor, Wade Miley, Rich Hill, Ryan Yarbrough, Aaron Sanchez, etc. Any of them could be the next Jorge Lopez.
Here's another example: Chad Kuhl. He has been a 5th starter for several seasons and isn't getting any younger. His fastball is well below average in the rotation but could play up in the bullpen if he adds a couple MPH. His slider is decent and he gets a lot of spin on his curveball (though his curve does get hit hard when it is poorly located). Get him to stop throwing his awful sinker (which he threw 44% of the time) and his changeup (which gets hit like crazy) and focus on what he does best.