The answer to this question is "as much you can afford". Because SFI is an open business where you are your own boss and you can have as many affiliates you need in your downline. So the goal must be set by you as to how much you want your business and should plan your expenditure accordingly. And if planned nicely, SFI is a place which gives you 100$ or even more for a single $ spent towards the business.
So, I would say saw a seed today and reap 100 tomorrow.
Best Luck..!!
