What self respecting gamer doesn't have a PS2. Also, most KH fans probably started with KH on PS2. Not seeing what you're trying to say here.
Okay....assuming every KH fans does own a PS2 that still leaves GBA, 3DS, PSP, mobile phone, then the games themselves.
No, because the GBA game was ported to the PS2. Meaning now, all you need is a PS2, a 3DS, and a GBA. Still not a fortune. And for the mobile phone game... no one played that, and it has next to nothing to do with the series.
PS3/Vita PSN: kewldude475; 3DS FC: 4253-3798-3218; Steam: kewldude475 Now playing: Persona 3: FES, Assassin's Creed 2, Resident Evil 6