Looking to move out the closet - no jokes please.

If I were to build a 8 X 8 X 8 grow room in the attic (SE USA), what would be more economical? Pull cool air from existing central air system and house, or put small portable A/C in room? Exhaust and/or ducting from both out through roof vents. The Sharp portable A/C looks pretty good at around $400.

Pulling all that cooler air from the central air and house would drive that electrical bill up as that air would have to be replaced. Portables aren't that efficient, but with less ducting and it being purposefully deployed, it may be cheaper (cost of A/C unit excluded).

Obviously, need to insulate the hell out it either way. Attic has vents, but with summer coming on, 120+ degrees not out the question on ambient in attic.

Room would be split flower/vege with lights out in afternoon. But even at night ambient attic temp are, uh, through the roof.

Thoughts, guesses, or experience appreciated.