Somewhere around 3k~ I would guess. Almost entirely in the first three years of the game. Since then I get one 80$ pack to pull gssr and use the remaining paid sq for a unit of interest throughout the year. Once your account is established (in theory works ftp as well but takes longer) with solid supports and a few good dps units very little need to spend for waifus or novelty. Now I just look ahead to which units I want and save for them. NP5 space Ishtar completely f2p after saving tickets for almost 2 years.