In a nutshell, quality SEO takes a lot of effort and a lot of hours each month to do it right. There are dozens of tasks that are done each month. This takes time, skill, and costs to hire the talent to do this.
Some inspectors that think SEO is what it used to be often scoff at prices because they think it's easy and Google can still be gamed. That's simply not the case anymore. Or they don't realize the benefit of ranking highly in their local market.
The rewards from ranking highly and getting a steady stream of client-direct inspections can be in the thousands of dollars per month. The ROI is a no-brainer. It's all about understanding the investment that it takes.
The answer no one wants to hear is that it takes investment, patience and hard work. Just like anything else in life that is worth having. SEO is the toughest investment to make but often the most rewarding.