If you are going to start a new business and you need a site for your business then you need to buy a premium WordPress theme. Because you can set up your site at very minimum cost with WordPress. Actually, WordPress is free but you need to pay for its premium theme and your server. To purchase a Premium WordPress theme you just need to spend $59.
If you don’t want to setup your site in WordPress then obviously you have to buy an HTML template to convert it in some other CMS application.
If you have someone who can help you to convert your site into WordPress then you can buy the HTML version of that theme. So it totally depends on your requirement.