This looks like a more refined combination of two of my mods. Interesting idea.
If you want to workshop some improvment ideas, I'm open for messaging. I've an idea to implement a user generated cost function I didn't build yet.

What ideas do you have to improve it?

It was pretty tricky to make a general purpose algorithm to set the tech costs. I use the tech's depth in the tree, and I look at the tech's effects, and I look at the number of techs that depend on it. I mostly ignore automatically unlocking technologies because I don't know what to do with them.

I have a hidden feature that lets people write custom Lua in the mod settings to control the tech cost. I disabled it because I didn't think anyone would use it. It's also very annoying to debug typos in the settings because they block the game from launching to even give you the chance to fix them.

My idea was to load a math function the player inputs, and then use pcall to pre calculate all possible values needed. If it failed, fall back on a pre defined behavior.

For my use case it's simpler, since I only have 1 variable to use (depth in the tech tree).

I decided that if I made a feature like that I would probably get flooded with mod compatibility bugs or "can you do this for me, I don't know coding" and that doesn't sound like a fun hobby. I thought the only people who might use a feature like that could make their own mods if they want to. They would probably prefer to make it themselves and just the way they want it.

I started out by only looking at the depth of the tree but it didn't feel fun. Some techs you're willing to pay more for, like getting robots and artillery, but others are dead ends or overly specific to a single mod. Like do you really want to pay a bunch for belt immunity, night vision, or defender capsules? There's game design questions to think about too. Should gateway technologies like unlocking a new science pack be expensive, or should the technologies that depend on it be expensive?

I think it's a trap to rely too much on procedural content because it feels hollow, so I added a bunch of little variables to give it a little bit of character.