There has been one recent player similar to Fultz that was traded during his rookie contract: De'Angelo Russell.
The Lakers got Brook Lopez's expiring contract, got off Mozgov's awful deal, and received the 27th pick that turned into Kyle Kuzma.
The Sixers do not have any comparable contracts to Mozgov right now, but generally, every 15-20 million is worth a late first.
In a comparable package, the Sixers would get multiple first round picks and an useful player on an expiring contract.
However, since Russell had shown much more production in the league than Fultz has, I think the most the Sixers could hope for would be a late first and a useful player on an expiring contract.
Ideas
Cavs trade JR Smith (partial guarantee next year) and Ante Zizic
Cavs trade Kyle Korver and a heavily protected 1st
Magic trade Terrance Ross and a heavily protected 1st