It depends on what you need. Different SEO services come with different rates, but the profile of your business is just as important. The best thing to do is reach out to a professional consultant and find out what they can do for you. A well optimized campaign is good value for money though.
Most businesses allocate around 10% of their marketing budget to SEO, so that’s another important consideration. SEO will cost you, but it aims to put your website among the first results in search engines and that’s where most people look. New customers will pay off straight away.