Deciding how much accessibility testing is realistic for a solo freelancer

I build small business websites on my own, and I want them usable by people who rely on keyboards and assistive technology. I can check semantics, labels, contrast and basic keyboard navigation, but I can't reproduce every browser and screen-reader combination. What minimum hands-on testing would you prioritize before launch? I'm trying to make accessibility part of routine QA rather than a vague promise at the end.