about 1800 seals? But i'd say it has changed since random Itachi frags have been appearing through free draw with no rare attached.

It's more. You get 1-2 frags each 60 draws in every treasure on average. So it's anywhere between 2400-4800 draws used(best and worse case scenario). Edo treasure USED TO have higher itachi drop rate (1-2 every 30~40draws) and was the "cheapest reliable way" of getting multiple itachi frags at once, but it was changed to match other treasures

Additional info which might be helpful:

Now since we have 5 treasures (kage, edo, lol, jin1, jin2) and pulling 60 free draws in a treasure takes ~120days, every 120 days you get 5-10 free frags, provided you dont miss a single free draw. So free draws quite substantially reduce overall time you need to draw all itachi frags.

60 x 80 = 4800 scrolls if you get 1 frag

2400 scrolls if you get 2 frags, so should be somewhere between there

My current 52 frags from est total SS

960 Kage

200 Jin 1

200 Jin 2

200 Kumo

200 Edo (This assumes from how many rare I have obtained. I hardly pulled from this one)

1760+ I only have 52 frags so far. I'm guessing another 1000 ss to complete.

I want Itachi also. He's such juggernaut. I'm leaning towards to finish him before I draw GNW. I might have another Kage Super Rare when I'm done.

something between 2400 and 4800.