Other Monthly Costs (i.e. EC2, private machines, employees)
Everything in this column is per month:
Number of Paid Users:
Number of Free Users:
Revenue Per Paid User:
Revenue for all Paid Users:
Cost per Paid User:
Overall cost of Paid Users:
Cost per Free User:
Cost of Free Users:
Other Costs:
Results
This calculator only accounts for S3 storage pricing. Storage pricing details are available here: http://aws.amazon.com/s3/pricing/. The S3 pricing it uses is $0.0275 per GB as a base (the lowest cost from any region using standard storage pricing. This doesn't take into account costs for Data Transfer from S3 to non EC2 machines, cost of processing files, cost of storing metadata, costs of CDN's or reverse proxies, or any non-product related costs. It also assumes that users pay $9.99 per month instead of paying $100/year ($8.33/month) as well as assumes there are no transaction costs. This calculator makes a lot of assumptions that tend to favor Dropbox. You can offset this by adding other monthly costs.
Edit: Calculator was modded on 09/29 to use standard storage(0.0275/GB) as a base instead of RSS and use 400GB of space (default value -- can change) per user instead of 500GB