Look around for various bonuses. We opened a Roth for my wife with $6500 which got her $100. I believe that a tax advantaged account has a lower threshold for money. If you're looking to refer someone else and collect money in your own account, TDAmeritrade has that. I refered my wife, put $6k in and received (from memory) $200 into my account. I believe I got $100 for opening my own account there with $25k, so the referral was way easier to get.