An SSL certificate ensures all information transmitted to and from your website is protected from third parties attempting to access it. It is important because browsers, like Google Chrome, mark pages without https and the green padlock in the address bar as not secure. This can have a negative effect on the trustworthiness of your website. Pages that are protected with SSL receive better search engine rankings, and are more likely to be trusted by visitors.
Moving to another website consists of transferring the website’s files and databases, configuring your site with the new host, and directing your domain’s DNS to the new host. Once you pick a new site host, they can usually help you out with this process. The cost will depend on the host you’re switching to, but it will probably be anywhere from $150-$400.