Maybe i worded it wrong but i mean its harder to, i know you can emulate it but i never found many PSX emulators to be worth my time in figuring out. Although admittedly i dont really search for PSX games alot since all i do is search for anime. >_> So i dont really know how hard is it, i just know ROMs in general are easier to find for me anyway.

So yes i would buy the PSX game first if it was up to me, and get the GBA later on ROM/EMU if you cant buy it later.