If you are planning on hosting the textbook on a website, one easy, cheap solution would be to use Github pages. This allows you to build a website within a repo and host it for free through Github. There are various levels you could go with this, you could do the HTML and CSS yourself, or use a template such as this which does a lot of the work for you. The only cost to using this is purchasing your own domain name, otherwise everything is free
If you are planning on hosting the textbook on a website, one easy, cheap solution would be to use Github pages. This allows you to build a website within a repo and host it for free through Github. There are various levels you could go with this, you could do the HTML and CSS yourself, or use a template such as this which does a lot of the work for you. The only cost to using this is purchasing your own domain name, otherwise everything is free