I did some reading. Don't go with the cheap plastic injection molds. Apparently they can bust easily. Think about hot, molten plastic under pressure.....then....*not* under pressure flying through the air. Uh.....yeah.....no good.
I did read up on making some molds from plaster of paris. Seems extremely easy and only costs a couple bucks (if that). Better than $40+ on an aluminum mold. Only drawback is if you drop the PoP mold, it's broke. But you can always make another.
One question though. I really like the black/blue swirl senkos from Yum!
I would assume you just pour one color, let it sit, pour the next color, let it sit, and repeat. Correct? Does the plastic need to be completely set or does it still need to be somewhat molten?