The Bulls payroll is under 40 million currently. To add Wallace/Garnett and subtract the players involved in the Garnett trade (Chandler and Gordon) the cost would be somewhere around 20-25 million.
Apparently the Bulls can't afford to have a team salary of 65 million next season. Even though the team is one of the most profitable in the league.
This 'Reinsdorf is a cheapskate' thing is becoming more and more wrong each year.