Don't worry...
FAA FY2015 budget: $15 billion.
DoD FY2015 budget: $560 billion. Cost of satellite upgrades amortized over service life: $366 million per year.
I think the DoD can afford it.
As a comparison the FAA spends ~ $220 million a year to maintain "legacy" navaids (VOR, NDB, ILS, etc.).