The Adobe Spark Starter Plan, both the website (spark.adobe.com) and the iOS apps (Spark Video, Spark Page, and Spark Post), are free. Yep, we said FREE! You can create, edit, share, and tell the world how much you love Adobe Spark. (OK, that last part is optional, but we won't complain if you are overcome with the need to share the Spark goodness).
The full version of Adobe Spark is a paid service that sits on top of the Starter Plan and lets you create branded stories with your own logo, colors, and fonts. It is included with every Adobe Creative Cloud plan, or available for purchase as a stand-alone plan either on the Spark website or via in-app purchase in the Spark iOS apps. Pricing is $9.99/month with no annual commitment, or $99.99 per year.
You can find more information here.