A good starting point is the graph below from the Bipartisan Policy Center. For an order of magnitude calculation, let's say 2 million federal employees and contractors aren't paid (maybe a bit high) until the debt ceiling issue is resolved. If the average daily cost to the government per employee or contractor is $200 a day (maybe a bit low) then about $2 billion a week is deferred. Then if we assume the federal deficit of about $2 billion a day (The non-partisan Congressional Budget Office estimated the FY2013 deficit would finish up at about $640 billion), it takes a work week of salary deferrals to buy a day delay of the collision with the debt ceiling...which is not a lot. So, starting now, the Administration has to negotiate both issues because the clock is ticking with or without a "government shutdown".