Cloud AWS Architecture

Could anyone please help me understand, on the AWS pricing page, there is the following statement:

Additional AWS infrastructure costs may apply. Use the AWS Pricing Calculator to estimate your infrastructure costs.

Would these additional infrastructure costs include:

  • SQL deployment: EC2 + Postgresql OR Aurora
  • Hard drive for the initial gateway??? The options show various machine sizes but no hard drive.
  • Other considerations? Backups?

Anyone with actual experience deploying this I'd really appreciate you chiming in.

thanks!