The issue is that if you identify yourself as a "hobbyist", this implies that you see yourself as a member of a group which is typically time-rich, cash-poor, and for which learning new skills and making stuff yourself is the norm. Hobbyists don't get products designed for them; they do the design work themselves.
The alternative is that you are a business, with the resources to get a product developed, tested, approved, and put into production.
The distinction between the two may be entirely a matter of commitment and perspective - but you do need to decide which camp you fall into.
If you don't have the skills and knowledge to develop your idea yourself, then you need to hire people who do have those skills at normal commercial rates. If you can afford to do that out of your own means, then that's great.
If not, you may need to go to your bank with a business plan, and take out a loan to cover the start-up costs for your business, which will include R&D costs, insurance, testing, approvals, tooling, manufacturing, marketing, advertising, and so on. That's what banks are for; to assess whether or not a business proposition is likely to generate a profit, and to fund or decline it depending on the outcome of that assessment.
It may be that you can partner with an engineer who will provide skills, time, effort and IP in return for a stake in the business. The size of this stake will, of course, have to reflect the true commercial value of the work which the engineer has done, multiplied by a factor to account for the risk that the project may not be a success.