You shouldn't productise anything with ESP32, its just an overprized bloated hobby pcb.
See my comment below on how to productize this: use a 4 cent off the shelf microcontroller on a 10 cent pcb or much better: make a custom chip with all the sensors on board but with $25K minimum Capex but tiny Opex
This is silly and reductive. You make different design for manufacturing choices at different steps of product development and volume.
In some cases, you may luck out and find that a widely available dev board is actually a really good match for your needs, in which case, run with it. You'll cut out a lot of NRE and get your product in customers hands faster. Once you've shown that you can sell in volume, do a DFM pass for V2 to minimize cost. OP probably fits this case, as all they need is Wi-Fi and Bluetooth, depending on their eventual power solution.
If you find that you're taking a dev board and soldering a lot of extra components to it, then I agree, you want to move to a custom PCB before doing any real volume. But you still might make a dozen first cuts with this and a 3d printed case to see how some product beta testers respond.
I'm certain that an ASIC wouldn't be cost effective for all but very large operations. Even if you could get it at the same price, it would massively increase time to market, and if you need to scale production fast you're shit out of luck. Not to mention you'll probably need multiple iterations, especially if you're sticking a Bluetooth modem and a bunch of sensors in it.
Using an off the shelf MCU and off the shelf sensors saves you all those headaches.
As others point out: you could hire someone to do it. Based on my custom 1 cent ASIC (custom chip) I would design, test and build your (moisture or other) sensor for €3000 excluding tax and price of all the needed tools. Usually more like $6000 because they want to outsource all the problems (like mass production and sales) to me
it is not a joke, you can do as low as 1.10870 cent per custom chip or 2 cent per off the shelf chip. 0.03 cent is impossible, the minimum size of a chip is .625 mm2 and that sets the minimum price.
Designing one for $3K is possible because I already have a tested chip design that I just have to modify for you.
A master student project is usually a free design with a free tapeout at Google MPW, Mosys of Europractice.
You seem like a very smart and capable person, and for an industrial buyer your proposal makes a lot of sense. For a hacker (who is often a hobbyist or amateur looking to build something simple quickly) a versatile SoC at $5/unit also makes a lot of sense.
I have to say you are hurting yourself with your communication style, because it comes off as very dismissive and arrogant. I bookmarked your presentation in case I need it in the future, but a 4 hour video is not a great way to hook people who are not sure if they are interested or not.
if you like to know more about it: morphle at ziggo dot nl to make a video conf appointment and get a demo. Or ask email questions, but that takes more effort for us both.
You're selling yourself drastically short asking for just 3k unless your plan is to wrap the entire project in a week. I don't think I've ever managed to even setup a new tech library in under a week, let alone design and verify anything.
See my comment below on how to productize this: use a 4 cent off the shelf microcontroller on a 10 cent pcb or much better: make a custom chip with all the sensors on board but with $25K minimum Capex but tiny Opex