To buy the Business Edition, click HERE to go the Silhouette Store. Click on the arrow to pull-down the menu under Silhouette Studio License Keys and you'll find the Business Edition.
The list price of the Business Edition is $99.99 but it actually includes the Designer Edition (DE) too. If you already have the Designer Edition, the store automatically takes off its $49.99 price so that you only pay $50 for the Business Edition upgrade.
If you are not sure if you need the Business Edition, you may want to check out the following chart. It shows the features of the basic (free) Silhouette Studio software, the Designer Edition upgrade, and the Business Edition upgrade:
One more thing, to use the Business Edition, you would need to download and install the latest Silhouette Studio update (v3.3.277). Click HERE to find out more about the software update and HERE to get your Business Edition upgrade.
P.S. I'm not affiliated with Silhouette America.