To me it is quite clear that infrastructure cost increase alot from each era, I decided to look closer to this increase and here is what I found by putting all information from the wiki into a google document which can be accessed here: Humankind infrastructure cost and please do so if I made any errors or you want to use it for some purpose to improve the game. 


Overall it is quite clear that the industrial era infrastructure cost too much compared to previous eras, the cost from early modern infrastructure to industrial era infrastructure increase more. both in total cost of building all infrastructure as well as average infrastructure cost and this curve could be made smoother. It is also worth to mention while cost of infrastructure increase, the power of infrastructure tend to stay the same, like a industrial era coal plant is something like 15-20 times more expensive than an ancient era forge but only give somewhat more industry than the forge. This cost increase of infrastructure also discourage development of technologies as the price vs payback increase. 


First is the total increase of infrastructure cost, the industry cost you would need to build all infrastructure of a specific era which are these numbers:

  • Ancient Era = 3340
  • Classical Era = 5290
  • Medieval Era = 9340
  • Early Modern Era = 16590
  • Industrial Era = 52230
 

As can be seen the total industry cost of the infrastructure don't even double per era before the industrial era in which it increase more than 3 times which seems very dramatic. However each era have different amount of infrastructure, so let take that account and instead look at the average cost per era, which are these numbers:

  • Ancient Era = 238,5714286
  • Classical Era = 440,8333333
  • Medieval Era = 1037,777778 
  • Early Modern Era = 1508,181818 
  • Industrial Era = 4017,692308 
Again we see a dramatic increase in the industrial era, the average cost of an infrastructure in industrial era is nearly 3 times as much as early modern era. Another big jump is classical to medieval. The jump between ancient to classical and medieval to early modern are smaller. Last we can look at the ratio of increased average infrastructure cost from one era to the next and it look like this:

  • Classical Era = 1,847804391 
  • Medieval Era = 2,354127284 
  • Early Modern Era = 1,453280125 
  • Industrial Era = 2,663931006 
The average industrial era infrastructure cost 2.7 times as much as the average early modern infrastructure, which is the biggest jump, the smallest jump is from medieval to early modern infrastructure in which cost only increase by 1.5 times.

This article uses material from the “Infrastructure” article on the Humankind wiki at Fandom.