Free money is mighty appealing. Would you open a new bank account for $50? How about $100? A number of banks and credit unions will pay you that much or more to become a new customer.I reviewed this issue of how worthwhile bank bonuses are. I also published a poll asking readers how big the bonus has to be to make it worthwhile. 29% of those who replied said the bonus has to be at least $200 to make it worthwhile.