I'm not sure if this is what you're looking for, but in column 204 or 203 depending on which DBC editor you are using. If your DBC columns start at 0 then it's column 203. That column is the mana percentage cost. Which should take a % of the players total mana. So if a player had 50,000 max mana, and you had 10 in that column then casting that spell would cost 5,000 mana I believe? I may be wrong though.
You almost right, but that column of % mana using not maximum player mana but Base mana from "player_classlevelstats" table basemana column...
i think i need find the function where it checks that info from db and change to player max mana constant, but i can't find where to do that :/
Sorry, checking right now spell.dbc i think i found it i'll repost in half hour.
uint32 manaCost; // 42 m_manaCost
uint32 manaCostPerlevel; // 43 m_manaCostPerLevel
ManaCostPercentage; // 204 m_manaCostPct
And yep still uses Base mana not max... :/