to be honest, i got the information from casual discussion with customer engineers. they did not reveal the cost but indicate although the cost is higher, manufacturing cost is not that many times more. he did mention for newer sensor the cost of r&d is high and equally important is the processor that decode the sensor reading. these processor arent cheap to r&d and manufacture either.
i did not mention the entry level cam is better than 600D, 60D or 7D. i just mentioned the price point can be between 600D & 60D to consider entry level and can salvage sensor & AF unit from 5dmk2 & 7D and using a new digic processor with some function unabled. having a ff dslr does not equate to be better than 60D, 5Dmk2 or 7D. Like what avsquare highlighted above, a lot of the feature are just down to the basic (the min) so for a user who needs good iso performance on non demanding situation, this is an option.
i do agreed your point on the popularity of mirrorless. if fuji compact F30 is a good reference, there is a lot of photographer desire for a good iso performance in compact than lens range, f-stop & so on feature on a compact. so in my opinion, a dslr with good iso performance at entry price should be popular as well and lot of us may only need the basic feature for our usage. so u got a good lens (better than most compact), the next logical thing is to have a good sensor that can perform in most lighting condition.
Yes, R&D cost is high, but then I honestly doubt the the R&D techniques developed for one sensor format cannot be applied to another sensor format easily. Just like you, I have no numbers or reference to back it up, but what I am thinking is that it is pretty much similar to scaling a technology. Kinda like canon's gapless microlenses technology developed for aps-c(was 50D the first cam to "feature that technology"?), was applied to the 5d iii and 1d x. Modifications may be needed for scaling, but it shouldn't be that different. In that case, the cost of sensor will still falls back on manufacturing and the vol of sales.
Again, an entry full frame, if there is such a thing, need not be better than a 600D, 60D or 7D, but the question is HOW DO YOU MAKE IT WORSE OR EQUAL? Read my previous post. There is really nothing much you can strip out of a 600d or 60d without removing bare necessities. How then, would it be possible to put in a more expensive sensor but yet sell at similar price? Lets say canon could slap in a ff in a xxxd body(which again, is totally impossible considering the vf and mirror box) and sell it at 60D price, why should canon do it when it will be canabalising the 60D market? Plus, lets not forget that the "ff in a xxxd body" is probably going to have a smaller profit margin than a 60d. Anyway, how can a camera with the 5d ii sensor and 7D af not be a better camera than a 60d?
Ok, you may say we could recycle back old technology, like the old 5D classic 12mp sensor. That is, assuming that it really is cheaper to produce a older 12mp ff sensor than a modern ff sensor. In that case how is canon going to market the camera? General consumer perception is simple. Nobody gives a hoot about how big the sensor is or how great the high iso is. Most consumers probably haven't heard of terms like metering and dynamic range. Consumers will only ask, "why should I spend $1200 for a 12mp camera, when the 18mp one is $200 cheaper and smaller?".
Or perhaps, we can look at it from another perspective- How much features can you remove from a 5D mark II to cut the price by half? I mean it is not like it has 8fps that you could reduce to 3fps so that cheaper bouncy mirror box and smaller buffer can be used. It is not like it has got a 50 pts cross type af points that you can reduce to 1, or a 100% viewfinder that you can reduce to 95%. It is not like on a 1D, where there are many features you can remove to create a lower priced product in the family. The 5D series is, essentially, already stripped down. Further removal of features will be like removing electric powered mirrors, air conditioning, radio, carpets and spare tyre from a car of year 2012. Some possibilities I could see are the alloy body, secondary dial and joystick, top lcd, penta mirror vf...but can removal of these features really drop the price from 3k to 1.2k?
I totally agree if we are talking about the possibilities of an entry ff going at 2k in the future, but I honestly think that an entry ff going at xxd price is really just impossible in the near future.