SEO is the process of updating your website and its content to improve its ranking on a Search Engine Result Page. While Google doesn’t charge for SEO, different professional SEO agencies charge their clients in return for their services. SEO is a lengthy and complex process where SEO agencies must refine the entire website to improve its ranking.
These agencies have years of experience making a website rank high. They have also learned the formula that boosts your website's visibility and increases your visits/sales, improving your ROI. While most SEO agencies have a fixed price, they can change depending on the size of your website, the time you are hiring the company for, and the complexity of the work that they have to do. You can always ask for a quote before deciding whether to hire the company for your SEO needs.