ghoultree havengul lich cast from graveyard magic

[lasercannon]

if I cast ghoultree from graveyard (for example using havengul lich)

would ghoultree count itself for subtracting the cost to pay?

[Arix]

No. The first part of casting a spell is moving it from wherever it is onto the stack, meaning that by the time you determine costs, it's not in the graveyard anymore.