$4k might not be that far off the mark given that a used IQ180 barely gets to $15k privately.
If I were in the market for a DB at the moment, unless I absolutely had to have it right this minute, I'd keep my money in my pocket. Why? Well, it does seem to be a tricky time to price the things - there seems to be a degree of uncertainty since the D800 hit the market, with a notable number of DBs coming up for sale and prices flip-flopping around all over the place. The fact that the IQ180 I mentioned above barely reaches 30% of it's new value just one year ago (and it was being sold by a top-rated ebay seller) is pretty astonishing. Kinda like saying D800s will be going for less than $1k in 12 months time. Er, I don't think so. Tests like the one they did on the circle of confusion website, where they banged out 60x40 prints (and that's inches, not cm for crying out loud) from an IQ180 and a D800, and had difficulty telling them apart, don't help either if you're a seller looking to recoup some $.
That is not correct. USD15,300 is where it is at, but reserve has still not been met. The BIN is at USD34,500. I know someone who got really lucky and bought one for USD30k, but that was about as low as I have seen it.
For someone who is not in the market for an MF system, the D800 may seem like a viable alternative, but I do not think it is rational to compare different systems and format. However good m43 and APS-C systems may get, they are still different formats from from FF, as FF is from MF, just as 645, 6x6, 6x7, 6x8, and 6x9 all render differently.
A souped up Mitsubishi Evolution does not a Ferrari make.