The "commander tax" is 2 for each previous time you have cast a given commander from the command zone this game, regardless of whether that commander was cast or is being cast as a creature spell, a planeswalker spell, a sorcery spell, or as something else (C.R. 903.3, 903.8; see also this thread and this thread). Remember that being a commander is "an attribute of the card itself" and is not a characteristic (C.R. 903.3). Notably, even a sorcery spell can be a commander spell, as in this case.
However, if you cast your commander from anywhere else than the command zone (including your hand), the "commander tax" doesn't apply (C.R. 903.8; see also this thread).
However, if you cast your commander from anywhere else than the command zone (including your hand), the "commander tax" doesn't apply (C.R. 903.8; see also this thread).