This question is about whether such general-purpose manufacturing robots are physically possible, not whether they're cheap or easy to build.
If given an adequate power source, the requisite atoms, and no unnatural obstruction such as an unusually strong electromagnetic or gravitational field, a sufficiently-sized group of such robots must be capable of:
Building an equal number of copies of themselves in under 1 hour.
Building any physical object in less time than it would take our current human civilization to build it. (Not counting existing high speed factory assembly lines and such.)
Each robot must be at most 1 milimeter long in every dimension.
The market resolves once our knowledge of physics and engineering is sufficent to have a definitive answer to the question.
The goal of this market is to asertain whether something like the "self-replicating nanobots" of science fiction are possible. The sort of robots that could easily wipe out humanity, terraform planets, and act as the ultimate manufacturing system for whoever controls them. I reserve the right to modify specific criteria of the market in order to keep it in line with that intention.
@EliezerYudkowsky 4 billion years is quite a bit longer than it would take our current human civilization to build any given object.
@IsaacKing How many steps removed is the final product allowed to be from the bots? With arbitrarily many steps, it seems trivially possible to manufacture anything humans can make (though not necessarily faster), since you could just implement a Turing machine and run an AGI on it.
@adele Yeah that's fine. If the nanobots can build a functional computer, I think it's a safe assumption that they can build anything else.
@IsaacKing You've suddenly made this question a lot less interesting. A functional computer can be made with a wide variety of materials and processes. And the most basic tools for macromanipulation are even more flexible.
At this point being faster than humans really depends on the tools the humans and nanobots start with and the optimization power behind them both to be able to design the process to build the object.
@Imuli I don't really see how this makes things less interesting? If the nanobots impliment an AGI, how does the AGI begin building the thing unless it's directing the nanobots to begin construction?
@ScottLawrence If the scientists are confident that the proof is correct, yes. I'd even accept a non-formal proof, in the form of a strong scientific consensus that it's possible. (Similar to how everyone agrees that sending a human to Mars is possible in theory, despite it never having happened yet.)