The self-hosted version is completely free of charge, while the version hosted by LimeSurvey comes in free and paid versions.
If you are using Nextcloud, the Forms extension is a good option for creating simple surveys and questionnaires. Survey info and responses are kept private on your Nextcloud instance.
Webform is a free open source form software, available to either self-host or host on Webform.com. The version hosted on Webform.com comes in free and paid versions.