You do not have to spend real-world currency to access Mari's Secret Shop, the majority of people "paying" for materials are using the currency exchange to convert gold into blue crystals. :
An idea for a small but significant improvement for the Currency Tab - an option to disable autocombining currency shards : r/pathofexile
Currency rates poe | zaasunzate1981's Ownd
General Discussion - Path of Exile Currency Calculator - Forum - Path of Exile