One issue I see in your messaging is that construction people usually do not speak like "completely offline, no cloud, no accounts, no subscription". When doing work for SME's one of the things I enjoy most is learning systems, tool chains, nomenclature etc... The above reads like a dev harvesting for leads.
I think people will understand it easily. It's like buying a really nice tool (which I do often). I will spend 300-400 dollars on tools I can have forever. It's easily justified if it makes my job easier.
A completely offline, no subscription lifetime app is an easy sell and exactly what people like me want.
It turns out...that's may be the easiest part. Google has successfully gatekept that last 10 percent of launching.
Though even this wasn't that hard... I easily found more volunteer testers than I needed on a relevant subreddit (the app is a PvP stat tracking app for a videogame, and I found plenty of people willing to sign up to test my app on a subreddit dedicated to that videogame).
That said, because of the unique testers requirement it was a much bigger pain in the ass to get listed on the Play Store than the Apple App Store (my app is written with kotlin multiplatform and supports Android/iOS/Windows/WASM).
Apple was much easier, pay $99 and 1 week later it was published.
I think Google did it this way to put some sort of filter on the amount of submissions without having to spend much time manually reviewing everything, foisting things on to the developer.
That's the exact approach I want to take though, kotlin multiplatform.
I've worked on construction software systems. Wouldn't mind an off-line chat.
In one sentence, no one (with skill) will work for you for free.
You might think $10 an hour is fair. Or you might think $1000 an hour is fair. If the developers you're trying to contact can't guess where you are on pricing, they'll probably ignore you.
I don't really need a technical lead...they would have no understanding of what I made or why it would be useful.
I've tested it in the field and I know it works for exactly what I want it to do.
I would suggest you organize your thoughts and write down the list of what you think you need and then either pay for a consult with a senior developer or chat with a trusted technical person.
From your posts, it sounds like you need more than one role and/or the services of an agency. If money is the issue and you think you have a good idea, then I suggest you seek funding.
I'm confident my product is worth it's salt in my industry, but lack the expirence for a proper deployment. If it issuccessful, a iphone port would come next. I do not have the hardware to properly test like I would want to and would want a professional to be in charge of capturing all the functionality of the android varient.
And if I may offer some more advice, it sounds like you need a technical co-founder as you're describing multiple roles and skills.
And what exactly do you want from the person, do you want them to build their app?