I have been developing a platform of wearable products that are reaching what I feel are their end-of-prototype stage. As shop prototypes, they are rough and unpolished. As a software and embedded engineer guy, I'm not hip to the final beautification process of the hardware, though I have an idea and expectation of what I want the products to end up as. What role does this? What firms do this?
There maybe several product design agencies that may help you with what's design for manufacturer and assembly and get it made. You need to choose very carefully however which one is right for both you and your product.
If you are looking to do a free assessment you can try out devToM dev2m.com a tool I am helping build.
I am from a software background myself and have taken hardware products to market. Feel free to ask me anything here.
By end-of-prototype stage, what exactly do you mean? Is it on breadboard, 3D printed case, etc? Highly recommend listening to the Y Combinator Podcast Oct 12 2018 -- a conversation on Hard Tech with Eric Migiovsky of Pebble on how they got started :)
Id recommend building 100 or so in house prior to spending loads of $$ mass producing...this will give you some revenue, feedback, etc. You can hire a product designer on Upwork who can produce you 3D models and you can work closely with to get visually what you want. You can 3D print, silicone mold, contract manufacture circuitboards, etc relatively cheaply through online sites like 3dhubs.com, pcbway.com, then assemble yourself and sell them.
This is a great first step, and will provide you with tons of knowledge of the process. Your early customers are invaluable for validation, and will help you to understand if you have made any mistakes in the engineering design, etc prior to spending loads of $ on molds, time working with manufacturers building the wrong product, etc.
It is important to do this step because if there are any issues, it will cost you a lot to fix later on. Dont be afraid to pay for expertise on Upwork. You will save money, time, headaches, etc. in the long run (and its amazing how low-cost it is for subjects matter experts in their respective fields).
You will probably end up with multiple manufacturers building each individual piece (for a wearable you might have the circuitboard/brain, a case, and a silicone band for example). You wont have one manufacturer who can do it all (although you can find places that will take the individual parts and assemble, box, etc). There are websites like mfg.com which list out contract manufacturers, you can also just google "wearable contract manufacturer" and get some good first page results :)
Working with manufacturing earlier, rather than later, is better because it will save you loads of time and money in the long run. They will suggest circuit/component changes to save $, design feedback to make cheaper molds, etc. Very valuable.
A company like Product Creation Studio (Seattle) can help with your E2E product development if you want to just pay for this kind of service.
Prototypes are usually manufactured by an engineering firm (design and engineering). Different engineering firms specialize in different materials and technologies. The first prototypes often come at a cost many, many, many times greater than the product's eventual manufacturing cost once tooling and processes have been figured out for mass production. Part of the engineering firm's job can also be to help you figure out how to make mass production possible. The techniques used to make a prototype are often very different from what you'll need to make multiples.
Make sure you have an attorney's assistance with protecting your intellectual property, which may include any of the tools designed to manufacture your items. If a production firm has to invent a tool to make your widgets, if you're not careful, they could own the tool, and if you ever tried to leave, you couldn't use the tool with another production firm and would be starting from scratch. Remember that you cannot discuss your invention with anyone if you intend to protect it with a patent, until after you file your patent.
The design and production aspects of engineering new hardware may turn out to be your largest expense, even into hundreds of thousands of dollars, depending on how different it is from other stuff that's available. The parts you may need might also be someone else's technology that you need to license. It can get complicated very quickly. If you're really lucky, it'll stay simple.
I remember an example of the "world's thinnest watch" which invested almost $300,000 in design and engineering, and at the end of the day they lost all their money because the failure rate was greater than 50% for all watches manufactured, which couldn't be determined until after the manufacturing process was done, so they never got off the ground with so much wasted material and labor. They did everything right, but the engineering task turned out to be too difficult.
As has been stated, you need a product design firm. A decent one will sit with you, talk to you about your target customer and the experience you want them to have, and they create a computer solid model as well as, if possible, a 3D printed model.
At then end, depending on exactly what your product is, you'll get the 3D solid model designs which you will then need to get manufactured. (A hint here. Make sure you get the actual source files from the firm, and not just the OBJ/IGS/STL files from them.) The price for product design firms vary, but I think a budget of $10K would be sufficient to get something that would look fairly nice.
If your enclosure is plastic, the next step would be to get prototype silicon vacuum cast parts made up. That won't set you back more than $1000 for 20 parts or so, depending on size. You'll also need to paint those when they come. If you aren't skilled with a spray can, find a buddy at an auto body shop who will do it for a few bucks.
If you are dealing with rubber or other flexible material, then you should ask the manufacturer what they can do for prototyping. The costs and options here will vary, but again a few $K is a good bet. Justenter your material type with the word "prototype" on a search engine, and you can generally find information.
So basically, plan on a budget for the design firm, and then a budget for prototypes. Once you have good looking prototypes that everyone is happy with, then you can look at production molds for manufacture. That is where the real money comes in. Production aluminum molds for plastic parts cost around $10K each, and in a worst case scenario you may need one mold for each different part.
Just remember the electronics are cheap. The mechanical design is where the cost comes in. Prepare to open your wallet.