What are the costs?

The beautiful thing about being an Affiliate is that you have nothing to lose. You don’t pay an initial cost, there’s no money to lose. Of course, there are some investments regarding web development and maybe some paid advertising but in most cases the costs are minimal. Your main game, SEO, can be done by using free tools, for example google AdWords, and other interesting analytical tools that can put you on the right track. So ultimately it’s up to you how much you will invest in beginning this venture.