Hundreds of $$..... Start with family and Facebook. Family sign up for free so that's your best start. I ran competitions in groups of 20 on FB. Everytime I got 20 ($100) to sign up, I'd give away £5 to one of them. Took a while to get going, but once they saw it was genuine (Facebook is full of Fake posts) I was filling 20 spots a day.
Mene only allow you to collect $100 of referrals at a time, so spend that before starting again.