google's gemini api is generous with free tokens and handles longer contexts well. not as creative as the others but good for factual content.
hugging face has tons of free models you can access through their api, though quality varies. some of the open source models are getting surprisingly good.
if you're serious about seo content at scale, you'll probably need to pay eventually. the free tiers are more for testing than production. also remember to fact-check everything these models spit out and add your own expertise - google's getting better at detecting pure ai content.
what kind of topics are you planning to write about?