Molecular machines can make more molecular machines, which can make yet more molecular machines. While the research and development costs for the first such systems are likely to be quite high, the incremental manufacturing costs of a system able to make more systems like itself can be very low. Wood, for example, is a complex product made from tens of thousands of proteins and a host of complex molecular machines. Yet we think nothing of slicing a piece of wood into a convenient slab and using it for a table. While nanotechnology does propose to use self replication, it does not propose to copy living systems.
Living systems are wonderfully adaptable and can survive in a complex natural environment.
This is much more than we need, much more difficult to design and much less economical than simpler alternatives. Instead, nanotechnology proposes to build molecular machine systems that are similar to small versions of what you might find in today's modern factories. Robotic arms shrunk to submicron size should be able to pick up and assemble molecular parts like their large cousins in factories around the world pick up nuts and bolts and put them together. The Foresight community knew, even then, that nanotechnology was feasible. This allowed discussions over a decade ago about the best policies for dealing with this new technology.