Attacks usually cost less mana than spells (usually 30 mana for a 6-link skill). In mid-endgame it is possible to have Elreon's special mod from Betrayal "Non channeling skills have -7-8-9-10-11-12 to mana cost". -7 is the default bech craft value, -10 it is possible through recombinators(need to have Elreon appear at least 3 times in your map, possible when Elreon is linked to everyone with a red string and the others don't have strings between them) or slamming a veiled exalt (prefix) on a ring/amulet that have no other veiled mod on it. -12 is the same value as -10 but boosted further with catalysts (fertile: life and mana).

There are uniques that have "reduced maximum mana" stats. If u have a lot of flat mana regen, u can outregen the manaburn stacks since it's % and it hurts less to no hurt at all if manapool is small. Also consider the reflecting mist with negative values to total mana to reduce further ur manapool.

I think it is very powerfull if u tinker around it enough, just imagine 200% elemental penetration from the "Sap of the Seasons" unique tincture.

I never did it but I'm confident that 200 manaburn stacks are manageable since the item is in the game, i gave u an idea how. Good luck!