SEO services aren’t necessarily expensive, as it normally depends on what you need to do. Compared to other forms of marketing, SEO is cheaper. You can print flyers and hire people to distribute them, for instance. That will cost and you’ll reach a general audience, not a targeted one.
The same rule applies to radio ads, posters, or even TV ads. None of these things is targeted and will normally cost more than SEO. Furthermore, while it’s a monthly cost, SEO offers a natural approach that targets people interested in what you have to offer, so the ROI is higher.