SEO like any other service will have its cost providers at varied ranges with varied levels of experience and more importantly efficiency.
If you’re finding SEO overwhelming, I tell my clients to focus in 3 stages. First is the basics which includes technical aspects of tags, keywords and google connection.
The next stage is content around keywords, page optimization and content generation. And the third stage is competitor analysis and backlink optimization.
These first step can usually be done by yourself. But even if that seems daunting, then getting someone to do it for you is the only way. A semi-decent SEO professional who doesn’t overcharge should be anywhere between 1k-5k depending on pages & need.
Hope this helps?