I don't think you will be far off, based on current prices...my last couple 1911s this year were much higher than I paid four or five years ago when the 1911 program started. And they started collecting state sales tax late last year too. Combined, I paid about $450 more per pistol.
Someone posted on the CMP forum a few months ago that he spoke with a CMP admin during a Garand builders class last fall at the CMP HQ and was told their target pricing was around $4k. Expect anything rare or exceptional condition will go to auction on Gunbroker, like it does presently.