Let's be realistic about what they'd be trading for, given both the lineup and the "cap" constraints.
DH: Harper, Schwarber
1B: Bohm (Sosa), Harper [Hall], Clemons
LF: Schwarber, [Harrison]
If Harper plays 1B after the All star break, it comes down to DH/LF
If he stays at DH, it comes down to 1B
Clemons/Hall are LH 1B, Muzzioti/Cave LH LF.
So they'd be looking for a platoon RH 1B/LF - who'd have maybe 150 AB the rest of the season, replacing Harrison/Guthrie/Sosa in the lineup (Bohm plays 3B full-time)
If that's the case, you don't want to spend a high upside prospect for a short-term patch.
Next year they figure out where Harper will play (probably 1B) and build the roster around that decision.
What would pry a young OF away would be a SP, but unless you think Nola is going to be pushed down, you're trading for an upgrade at 5th starter, again, how much do you pay for a patch (12 starts, no playoff starts).