You should think about getting a good used cymbal for $100 (Zildjian or Sabian) it doesn't matter. What matters to me is the if you get a really good cymbal. Try to stay away from the cheap models like B-8, ZBT, Bronze, etc. Going that route will be a waste of your money. Keep your receipts, so you can get your money back. And if you're going to donate the equipment, you can write it off on your taxes.
As for the size, I would go with a 18". Nice full sound.