How can i figure an approximate average cost for my server?

To estimate the average monthly cost for each of your remote desktop servers, you have several options in AWS:

1. Use the AWS Pricing Calculator: This tool allows you to create detailed estimates for your specific workload. You'll need to know your server specifications (operating system, memory requirements, I/O needs, storage requirements, and expected usage duration). The Pricing Calculator will help you find the most cost-effective options for your use case and budget. For workload estimates like yours, this service is free to use.

2. Check Cost Explorer: If your servers are already running (as you mentioned you have 7 active), you can use Cost Explorer to analyze your actual costs. Cost Explorer can provide detailed breakdowns of your spending, and you can even enable hourly granularity data for more precise analysis (though this comes with a small additional cost of $0.01 per 1,000 usage records monthly).

3. Use Cost Optimization Hub: Access this through the Billing and Cost Management console. This tool analyzes cost efficiency and can help you identify potential savings opportunities for your existing servers. You can view your data in either chart or table format and aggregate costs by various categories including AWS account, Region, and resource type.

Since you already have 7 servers running, reviewing your actual costs through the Billing and Cost Management console would give you the most accurate picture of your current per-server costs, which you can then use to estimate costs for future customer servers.
Sources
Estimating monthly savings - AWS Cost Management
Generating estimates with Pricing Calculator - AWS Cost Management
Estimating cost for Cost Explorer hourly granularity - AWS Cost Management
Generate an estimate in AWS Pricing Calculator - AWS Pricing Calculator