A new D700 is $2200. A used D3 is $2800. A used D700 appears to be $1800 (no grip). $2800 is way off the mark for a used D700.
An undeniable paradox: To think that there is any such thing as an absolute rule is at worst naïve, and at best, shortsighted. There is no such thing as an always-true, all context- or situation-salient, absolute rule that always holds true…including this one!