The era levels are gated behind the "star" of your character, so you have to 7-star in order to max the era level. This is indeed very predatory in terms of prices. You also cannot do any F2P past the initial era levels, you can only progress by spending cash.
Given that you also have to wait for the era to end before using the character in actual game modes, the only real reason to invest in this is to obtain the materials needed for relic 10. You also unlock the character at a certain relic level according to your investment when the era ends.
CG's earlier post implied most F2P accounts would end the era around level 65 on the era level. Given that it costs money to actually progress I am not sure how that can happen. But level 65 would be equivalent to gear 12, so not on the relic scale yet.
I think it's a failed system, it is using an auction for relic 10 materials effectively as an attempt to increase earnings. I would never spend so much for the dubious benefit of relic 10. You will have to spend hundreds of USD per character throughout the era to really participate on it. Of course some will do it, but the vast majority will probably not engage heavily. Even for big spenders the fact that you don't unlock the characters before 90 days has passed, will have many on the fence looking for actual reasons to spend....
We will 100% see relic 10 required for new journey guides very soon to provide more incentives to participate on this system. It is turning ever more predatory