Yakumo Let me help straighten your brain out a bit.
80+20+10+50 = $160
160 x3 months = $480
9 packs of $50 spirit stones for 7500 (2500)
1 pack of $20 spirit stones 3000 (1000)
1 pack of $10 spirit stones 1500 (500)
So in three months I could have
9x 7500 (2500 permanent) =67,500 (22,500)
1x 3000 (1000 permanent) = 3000 (1000)
1x 1500 (500 permanent) = 1500 (500)
In three months of patreon payments I could buy 72,000 (24,000 permanent) spirit stones.
At 20 spirit stones a chapter I could buy 3,600 chapters here. Those are some expensive chapters too.
At 14 spirit stones a chapter I could buy 5,142 chapters.
That's three months worth of patreon payments for me.