The Sox currently have 101,000,000 dollars tied up to the roster, not considering Arb players and re-signing Papelbon.
Add 13 million for Paps, and it increases to 114,000,000. They should also have around $25 millions tied up in arbitration-elegible players (i'm overstating, just in case), which adds up to 139,000,000.
With a luxury tax treshold that should be right around 183 million dollars, that gives the Sox around 35 million to play with while staying comfortably under the luxury tax.
$15 mill for Beltran, $10 mill for Jackson, and you have around $14 mill to play around with for the bullpen, a bench player, and a couple insurance arms.
Sounds pretty good to me.