So the contracts are the following:
Durant (Cap Hold) - 25, 894, 800
Waiters/Foye/Mohammed/Fisher Cap Holds/Morrow Non-Guaranteed - 23, 369, 437
Westbrook - 17, 769, 374
Kanter - 17, 145, 838 (Can't believe Kanter makes the same amount as RW
)
Ilyasova - 8,400, 000
Oladipo - 6, 552, 960
Singler - 4, 837, 500
Collison - 3, 750, 000
Adams - 3, 140, 517
Payne - 2, 112, 480
McGary - 1, 526, 040
Roberson - 2, 183, 072
Huestis - 1, 191, 480
Total - 117, 873, 498
So renouncing their free agents, cap holds, and non-guaranteed contracts other than Durant, they'd have 94, 504, 061 in salaries. They also have Sabonis to sign and empty space cap holds, so if they lose Kanter that puts them at 76, 734, 687, which isn't enough. So then they trade Ilyasova to get them to 68, 334, 687, which still isn't enough. So then they trade Singler to get them to 63, 497, 187.
So you'll have 63, 497, 187 in salaries plus:
Horford - 26, 400, 000
3 empty space cap holds at 547,000 a pop - 1, 641, 000
This leaves them at $91, 538, 187M without yet signing Sabonis. Would they still have enough room to sign the 11th pick in Sabonis (has to be less that $2, 461, 813 if we assume that the cap is set at $94, 000, 000) AND have room for Durant without losing another player?
EDIT: If they wouldn't have to trade anyone else, they'd be left with this roster:
PG: Westbrook, Payne
SG: Roberson, Oladipo
SF: Durant, Huestis
PF: Horford, Collison, McGary
C: Adams, Sabonis
VS our roster
PG: IT, Rozier
SG: Bradley, Smart
SF: Durant, Crowder
PF: Olynyk, Mickey
C: Horford, KO, Zizic
Sure, their starting lineup is a little better, but we also have assets to upgrade that lineup even further with something like Noel. We also have a much, much better bench and supporting cast around our Big-3 of IT/Durant/Horford than their Big-3 of Westbrook/Durant/Horford, we won't handcuff our cap for next year and beyond, we won't mortgage our future of draft picks to open space up, and we're in the easier East. Even with them having Westbrook, there is definitely an argument that our situation is overall better with Durant and Horford than them.