I need only photoshop for iPad and I am a teacher. Which are the cheapest option?

Options include:

• Purchase the Photography plan from Adobe which includes Photoshop for iPad
  (any plan that has Photoshop includes the App)
  https://www.adobe.com/creativecloud/plans.html
  
  
• Purchase the Design Bundle from the App Store which includes several mobile apps:
  https://www.adobe.com/creativecloud/mobile-design-bundle.html
  
  
• Purchase Photoshop for iPad from the App Store 
  Same price as the Photography plan but without anything else

Jane