No, they would not pay an outside free agent that much money, as they showed us last year when several good DTs were available.
But, I am not convinced this story about being close to a deal with OSA is real. I think this close to free agency, Osa is going to test the waters and see what he can get. I also think he probably knows Washington is going to make him an offer higher than what Dallas can pay.
This might be good though. Maybe Jerry will be miffed about losing Osa and do something like sign Milton Williams to replace him. Williams grew up in Crowley, Texas so maybe he wants to come back to his home state and pay less income taxes to play for Dallas. Working in Washington he will pay up to 10.75% on his income, including his signing bonuses. That is potentially over $1 million. In Dallas he would pay 0.