"My gut feel is that mechanical shops in the US are in two categories: 1) competent, and running at 100% capacity or 2) incompetent, and running at almost 0% capacity."
Buying something mechanical in the US is disorganized. There's nothing like Alibaba's wholesale side, with a reputation system. There's ThomasNet, but it's just a big industry directory. There might be an opportunity here for somebody. But it's not going to be a huge business.
Designing something to be injection molded is hard. There are lots of little things that run the price way up. There's "Injection Molding Part Design for Dummies", which is $495 on Amazon, but Proto Labs will send you a copy for free if you ask them. Incidentally, all TechShop locations have a small injection molding machine good for about one part a minute, and a CNC mill on which you can make a mold. They even have Autodesk Moldflow, which helps design molds using finite element analysis to predict what will work. So you can make prototypes and learn what works.
If you're dealing with a mold-making shop, if you send them files in Inventor or SolidWorks along with a Moldflow analysis, you'll probably get a much better price. In mechanical, the more clueless you are, the more it costs.
EMachineShop has a nice little CAD program which knows what their shop can do and will price the job. It will tell you if they can't make something due to some constraint (sheet metal bends too close, hole too deep, etc.) and gives hints on how to make the job cheaper. Those guys have been around for about 15 years, do a nice business, but haven't grown much.
Your mention of Alibaba made me think of something. I believe the electrical manufacturing world is much more globally integrated than the mechanical world. I say that as a practicing mechanical engineer. A resistor, capacitor, chip are the same in US, Europe & China. On the mechanical side all have different material standards and industrial standards.
And here is the US's disadvantage there, we are still on an island when it comes to that stuff. Sure you can get some metric nuts and bolts here (in US steel grades). But try buying European grade steel here (nigh impossible). Try getting an EN (nee DIN) or JIS flange here (do-able but lots of calling around). Try finding an engineer competent in the PED or machinery directive.
In Europe and Asia they can get US materials and make to our standard and sell to us. But its much harder and more rare to make products here and sell them to Europe and Asia. Usually you are making a US product, and "proving equivalency" with the European and Asian standards.
TechShop is great for hobbyists with some money to spare (there are a lot of hidden costs, both time and money, that they don't tell you about), but terrible for professionals. Their machines are regularly not working for days at a time, and I've had experience with multiple locations so this is indicative of the company as a whole.
If you want to manufacture with plastic, I'd be surprised if there was any reason to do it outside of China. If you're working with metal, it's a much trickier question.
Along with EMachineShop, there's also Plethora. I've never used Plethora and it seems incredibly limited, but they've been around a few years and have a ton of people on staff (which can't be cheap) so they must be getting decent business.
Buying something mechanical in the US is disorganized. There's nothing like Alibaba's wholesale side, with a reputation system. There's ThomasNet, but it's just a big industry directory. There might be an opportunity here for somebody. But it's not going to be a huge business.
Designing something to be injection molded is hard. There are lots of little things that run the price way up. There's "Injection Molding Part Design for Dummies", which is $495 on Amazon, but Proto Labs will send you a copy for free if you ask them. Incidentally, all TechShop locations have a small injection molding machine good for about one part a minute, and a CNC mill on which you can make a mold. They even have Autodesk Moldflow, which helps design molds using finite element analysis to predict what will work. So you can make prototypes and learn what works.
If you're dealing with a mold-making shop, if you send them files in Inventor or SolidWorks along with a Moldflow analysis, you'll probably get a much better price. In mechanical, the more clueless you are, the more it costs.
EMachineShop has a nice little CAD program which knows what their shop can do and will price the job. It will tell you if they can't make something due to some constraint (sheet metal bends too close, hole too deep, etc.) and gives hints on how to make the job cheaper. Those guys have been around for about 15 years, do a nice business, but haven't grown much.