How much do regular players spend on Path of Exile?

I've heard a lot that you only need a pretty small purchase if you want to play Path of Exile in the endgame, but I also know there are a lot of tab purchases that make playing the endgame much more convenient, not to mention base stash space being pretty limiting.

What do you think is the minimum buy-in to the game, and what do you think regular players typically end up spending to play Path of Exile?