First, I am a big supporter of local manufacturing and shipping data rather than goods whenever possible.
I think there is a fundamental problem, you assume that if you can reduce shipping by transferring data to a another location then all other costs stay the same. You’re taking the “mass” out of mass production and that is where most of the efficiency is built in. I think you’re talking about makers and local fabricators and not necessarily factories but there are still purchasing and assembly efficiencies as well as material inventory issues to consider.
On top of that your rate of $4-$10 doesn’t go very far in covering any overhead to own and operate this machinery and if it does then it definitely doesn’t leave anything to cover the hourly cost of skilled labor setting up, babysitting and then assembling and packing out the job for shipment.
There may be a model here for sustainability and community but i don’t think it can all be wrapped up in a tidy package that also includes 70% cost saving.
if this is just about basic 3d printed and cnc cut parts you should check out 3dhubs