OK forget the rotor
~ for a moment
.
Weight:
Reducing the weight of the craft's components allows for more of the other goodies (safety, reliability, payload etc.) to be put in. The following is an excerpt from an article in this mornings paper entitled 'Airbus aims to trump Boeing'.
" the company [Boeing] plans to build the airplane [7E7] largely out of carbon-fiber composite panels, which are lighter and more resilient than aluminum, the material from which almost all planes are made today."
This large and ever increasing consumption of carbon will result in a continuing decrease of its cost. If the cost of the first prototype is a serious problem, one might consider the use of timed-out carbon prepreg, or fiberglass with an extra layer or two.