Erm..... You looking for first hand or second hand product?
And do you already have any FX lenses?
With a budget of 2-3k... and you're looking for D600 or D3..not say its not possible but i think its abit hard..unless u already have FX lenses.
If not you will be left with very little or no more budget for your lens. (I dont know about you..but in most cases..a lens is more important than the body..IMO)
So..If u dont have any FX lenses and with that budget..I honestly think.. Its better for you to buy a APS-C camera and mount a good glass on it instead.
Nope.. I only have oly lenses.. hmmm seems like im going towards apsc cameras.. unless I go for d600 and 2nd hand kit lens