- If you want the AWS dashboard metrics to have 1 minute instead of 5 minute granularity, that's $2.10 per instance per month. 5 minutes is pretty useless, so either you set up other monitoring or you pay a tax on the number of instances you have.
- If you use AMIs (which you probably should) to launch EC2 instances with all your software baked in already, you will probably end up with dozens or hundreds of old, unused AMIs. Furthermore each of these AMIs is linked to a snapshot, which is stored on S3. S3 pricing is very cheap but it's a significant amount of work to determine which AMIs are no longer in use and to delete both the AMI and the corresponding snapshot. Every 100 AMIs you have at the standard 8GB root volume size costs you $18/month.