Falk:
The RX1 has a street price of $2800, while the body only A7 is $1000 cheaper. You could say that for $1000 you're getting an excellent lens, and I won't argue with that. However, you're not asking Pentax to do it for more than a body-only 645Z, but
for less than half the price.
By the way, the cost of the sensor and its contribution to the final price are different things.
Wait, the 645Z's price is arbitrary, right? Convenient... but not acceptable, I'm afraid.
Pentax is indeed able to make a much cheaper camera, but there are factors working in their favor:
- not having to develop a complete electronics+software for the 645Z, instead reusing/adapting the ones made for APS-C
- sharing various costs with APS-C (e.g. production space, distribution, support etc).
With the very low volumes of the DMF market, I think that's a better explanation than "the prices are arbitrary"