The R&D outlay needed to copy the mechanical process of machining a fully manual camera is considerably less than what is needed to pump out 35mm CMOS/CCD sensors. It's not a matter of 5x as much, more like 5,000x.
Look, digital rangefinders are niche products, there is absolutely no reason for anybody to be making knock-offs. So few would be sold that there is no way they would be able to recoup the cost of production, especially without a brand name like Leica to help them sell. With so§ many rangefinders on the used market, there's no floodgate waiting to open, no multitudes of consumers just waiting for a cheap RF. Everybody who wants a cheap digital camera already has one.
The overwhelming majority of people who want cameras buy P&Ss and DSLRs. They already have what they want: autofocus, cheap lenses, etc. They will not flock to a non-exact, manual-focus system, they will not make the volume that they need to make a cheap digital RF viable.