Why do people think Cuban can get both Deron Williams and Dwight Howard? According to Hoopworld, Dallas has $37,968,577* already committed to players in 2012-13. They could knock $8.3mm off of that by amnestying Haywood or Marion next summer, but then they'd only be $28.3mm* below the likely cap of $58mm (which assumes league revenue will be steady). That's nowhere near enough to sign 2 stars. According to the new CBA guidelines 7+ year veterans can get 30% of the cap. So, Deron and Dwight could get a little over $17mm per. I don't see two free agents each leaving $12mm (over four years) on the table.
For those that dream of Dirk giving another discount to make this possible, Dirk is due $20,907,128 in 2012/13 and $22,721,381 in 2013/14. Splitting Dirk's salary with both FAs would bring the per-player salary up to a little under $17mm, and I'd be pleasantly surprised if Dirk forfeiting $10mm he already has under contract.
That said, I'll be ecstatic if they get one of the marquee guys. One player to take some of the pressure off of Dirk as he ages would be unbelievably important short- and long-term. I think the most likely to be available is Deron, if NJ strikes out on Howard. Also, if you're curious, here's the full list of other free agents for next summer.
Also, could we quit talking about Dalembert signing now? The Mavs can only offer min deals since they've dealt their exception, and a center like Dalembert won't go for that. If you think the Mavs should get him, use the trade machine to figure out how it would work on a $10-11mm deal. We're looking for guys that are unlikely to have large offers elsewhere.
*edit: I forgot to subtract Rudy and Brewer when first posted. Also, Vince Carter's 2013 and 2014 salary is partially guaranteed, so that will eat up a little cap space, too. Further clarification on potential star salaries was also added later.