You forgot cap holds for each player we are short of 12 players, at $500k per player.
The issue is that the amount of cap space we'll have is pretty near the value of the TPE. It's not difficult to get a S&T worked out for a $10 million free agent -- probably doesn't cost more than a 2nd round pick when you're not sending any salary back. And once you're talking Melo territory, you're probably going to need to do some significant trading to clear the room or just involve NY (although Jeff Green plus all of our non-guaranteed deals work to match salary, so then it's a matter of picks).
Melo is certainly possible. I just think that if he winds up somewhere other than NY, a sign-and-trade will be involved, unless Sam Hinkie is a mad genius and sells him on Philly.