Prices can change in lucky star so since lucky stars isn't this week, go look at on average what his price is there. If you're not on the discord where they posts prices, you can follow PickleJuicy on the forums to figure out cost per frag.

Here's the recent link of lucky star: https://forum-narutoen.oasgames.com/page/show-post-46628-1.html. Just multiply the cost by 80 to know the cost at 3*.