Before you start spending money, check this out first:
That will at least help you figure out which ones are going to be the most expensive/rare to find. I'm sure someone will give you a really fair deal here compared to anywhere else. I know a few people here bought a whole boatload of them. The orders are still shipping though so you might want to wait a week or two until everyone has them in hand.
Looking at that chart, I'm glad I'm not interested in Aerith or Tingle. I guess Ico is one of the semi-rare ones though. My chances of someone selling another one for $35 are slim (I'm jealous of the person that won).