Forget CentOS, who are taking too long with 6.x. Amazon AWS with Red Hat Linux 6.1 for $0.085/hour for t1.small is excellent and $0.02/hour for t1.micro is even more excellent for high-availability services.
For file backup services, the S3 reduced-redundancy storage for $0.093/GB is a steal, but make sure you convert your storage buckets to RRS. The Windows Home Server plugin does not set RRS so use an Amazon EC2 instance to run convert_to_rrs.py and quickly convert your bucket to RRS for big savings. The AWS console won't work on huge buckets, nor do the popular Windows-based S3 tools. This might cancel out some of the savings.