I noticed that the price of Wood is ~90 per unit, but that's super high for a common resource.

Is there a way I can change the item price? If not, can you add one?

I think prices depend on what combo of mods you are using, some mods add easier ways to generate resources making them cheaper and vice versa.
For example, a normal 1x steel-plate uses x8 iron-plates
if you use Angel's smelting and say theres a recipe that gives 4 steel-plate for the price of x8 iron-plates, that will lower the price of steel.

I don't think this should be called a bug.

Though I agree that support for adding custom prices would be wonderful, for example with my playthrough, I want physical currency that I can store in a warehouse and doesnt fluctuate, so I can simulate storing money on my factory, and then moving that money to the system if i need to buy something.

Having that capability would greatly increase roleplay potential when you want to simulate playing Red Alert + Factorio using Klonan's Total Automization + ITC
Sell "gold/ore" through ITC then buy units to use for Total Automization. Voila, Red Alert and Factorio made a baby.

Exactly. Every single recipe (except for those cheaty creative ones) are taken into account. If you want to change some of the base prices, you can change the values in the array in control.lua from line 70 to 79. Most of them are quite straight forward, but "base" and "base-fluid" are those items which don't need anything to produce, but don't fall into the previous categories.

Funnily, there is already a currency which won't fluctucate at all. Fish. I made it so it is stuck at exactly 42 credits forever and ever. I guess you will be filling warehouses with fish now :D

Yes! I'm currently using fish as "currency" after I've failed adding my coins to your mod.
Is there a way I can add a clone of the fish currency and call it Coins? I've failed every time I tried adding one, always showing coin as n/a in game.
If that's not possible I'll just edit the base game locale and change fish to coin + graphics changes.
I love your mod!