How to offer SEO to small businesses who cannot afford those many hours every month

Hi there,

I am a sole proprietorship web designer who is also very passionate about SEO.

I want to offer SEO to clients but I ask myself if this is a business that can actually work.

My thoughts 1. SEO is ongoing work, to get actual advantage of it a monthly investment is necessary 2. Small businesses probably do not have the money to invest that much 3. Larger businesses go to an agency instead of a sole proprietorship 4. Very little SEO work is almost useless and there won't be a ROI for the small business

Your thoughts and experience on that?