From the Document: "This letter responds to three questions you asked about the budgetary costs of higher interest rates and inflation. 'How Have the Congressional Budget Office's Projections of Interest Payments Changed?' [...] 'How Does Increased Debt Affect Federal Borrowing Costs?' [...] 'How Would Holding a Greater Portion of Federal Debt in Short-Term Securities Affect the Budget?'"
Congressional Budget Office: http://www.cbo.gov/