The trick? Find the right influencer in your niche so that you're targeting the right audience. It's not just about spreading your message. It's about spreading your message to the right consumer base. If you can do that properly, then you can likely reach a sizable audience for not much money invested when you think about the potential profit it can return.
This article includes a general overview of types of affiliates and agreements. Every business situation is unique, so be sure to get help from an attorney in preparing any affiliate agreement. There may be "gotcha" clauses or language that you may not have seen or included. For example, if you are the affiliate, check to see what percentage of ownership, if any, the other company has in your business.