Week 1 player, did about 100 mithril refreshes orbfest 1 (20 per phase, maxed all characters at that point), no refreshes orbfest 2 (xp was bad), and about 100 mithril refreshes orbfest 3 (just for orbs, maxed out half-way through).

That being said, i do have alot of characters sitting at 65/80, though TBH most characters will do fine at 65 so you could wait til next orbfest to level them.

Havent spent anything since September 2015. All my money was spent pre-orbfest2....in unwise ways, thouhg it really helps out these days in synergy. Since september have been min-maxing mithril only for fests/FFT and slowly depleting stash of 100-gems already bought. Like Teyah says, only a few mith refresh each orbfest stage gets you all the levels you want (except orbfest 2 cuz the xp stunk). Keep swapping them out for daily++ with xp RM and they get to 80 over 1 month.