Pretty sure Coincompare API is free as well. You will have to optimize most aspect of on page seo and page speed yourself. Below are my suggestions/recommendations for this theme. Also, you have to manually add coin pages in the backend, they don't show up automatically.
1. Improve upon coin price page. There should be some availability to add content between graphs/charts.
2. I don't know what sort of backend coding is there to support coin price pages, but they are not seo friendly, all of data is being pulled through API, but even if data is pulled out through external source, it