So I have some friends who just got endless legend. and we are playing a game. Does the increased cost of units per era happen when one person advances an era and it effects everyone? or is the era cost only determined for each player based on what era they are in? Reason i ask is I am in era 4 and one of my friends is in era 2, and made the comment about how long it was taking to make a settler. 

"is the era cost only determined for each player based on what era they are in?"

Yes.

Yeah, actually the base cost (before equipment) is based on the unit level, that increases by one with each new era.