OK, I started running numbers. I spent 25 years making computer chips, so I know a "little" about that end. Taking a look at the 3 DSLR size:

18 x 24 mm

24 x 36 mm

36 x 48 mm

Next, find the number of gross die per 200 mm wafer (still the main wafer size for sensors), it comes out at:

18 x 24 mm 55 gross die
wafer

24 x 36 mm 24 GDW

36 x 48 mm 10 GDW

Lets add a 90% die yield and a $1,000 wafer cost, we have a net cost per die of:

18 x 24 mm $20.41

24 x 36 mm $45.45

36 x 48 mm $111.11

OK, now we have good die on a wafer, lets add the cost to package & testing (AKA back end) I have less back ground in this, but will use SWAG numbers:

Die size Die cost P&T Total cost going into the Camera

18 x 24 mm $20.41 $25.00 $45.41

24 x 36 mm $45.45 $40.00 $85.45

36 x 48 mm $111.11 $75.00 $185.11

This is the fab and back end cost, it does not include the NRE (design and masks) That cost could be 10 to 25 million USD. Less use a NRE cost of $20,000,000. The amount that will be added to each camera is based on the total production run, I will use numbers of 50,000, 100,000 and 1,000,000. (this is why it makes sense for Nikon to use the same sensor in the D700 as the D3, and why Sony may want to sell it's 24 Meg sensor)

Production Run NRE/unit (based on $10,000,000)

50,000 $200

100,000 $100

1,000,000 $ 10

So the net cost to Nikon to make a MX sensor (36 x 48 mm with 100,000 units) vs a DX (24 x 36 mm with 1,000,000 units) would be $285 vs $95 or about $200 in it's BOM.

OK, I may be off a little, but it is not going to be $1,000's more to make. You can also see why Nikon will want to price it so it will sell in big numbers >
100,000 production run (in 18 months), that is a run rate of

OK, I did not talk about the cost of the computer processing needs in the camera, true, but if the Sensor is about 2X, then the computer power needed will be about 2X, that is the normal increase in 18 months (OK the D3 is not quit that old( it was per DPR Announced 23-Aug-07), but you get the idea, based on Moore's law ( which is for computer type chips NOT sensors!) So there is not a lot of change in that cost from when the D3 came out.

The retooling for the camera and lens is a different cost, that is not may area so I will let all the other talk to that point.

Mike