I guarantee you that, given your requirements, this will never be a product that you can buy.

Hardware projects live and die on scale. The engineering and tooling costs are a similar order of magnitude whether you make 1000 phones or 1,000,000. If you can guarantee that you have an accessible market for a million devices, then you're starting to get into the region of scale where this would be an OK idea.

Mind you, that's a million users who are cool with all the design tradeoffs you had to make to ingress protection, software performance with modern android, and form factor in order to get your desirable characteristic.

The Punkt MP02 is at roughly the price point and "niche-ness" as the product you describe here, and that sold for almost $400. They could afford to build in about the same amount of functionality as a Nokia brick of yore (but with 4G radios!) for that price.