With all the new pvp-oriented spells coming into the game ( obsidian colossus, inferno salamander, etc) with large spellement branches, I think they should cost arena tickets to obtain rather than be gated by a scroll of fortune event.
Overall cost for a completed spellement path would be in the ballpark of 5000 - 6000 tickets (so maybe 45/50 tickets per spellement reagent?)
It would encourage wizards to participate (and win) tournaments. In the meantime they will hopefully improve upon their pvp skills while also gaining progress towards buying spellements for their desired spell.
obsidian colossus, 
inferno salamander, etc) with large spellement branches, I think they should cost arena tickets to obtain rather than be gated by a scroll of fortune event.