My fee structure is proportionate; the more money you will make as a direct result of my SEO skills, the more money I charge.
If you are a dog walker, the amount of money your site can generate is limited, and I am more than happy to optimize your site, for a small, modest fee.
But if you are a factory in China shipping container loads of goods to the entire world, making millions of dollars thanks to my SEO expertise, I will want more than just a small, modest fee. I believe this policy is totally fair.
Therefore, I do not have a fixed price for my SEO services.