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I'm a big fan of Carbonite, and they just teamed up with Drobo to offer special pricing for small businesses a few months ago. It's only $229/year for 250gb of storage, and $599/year for 500gb of cloud storage, which is a ridiculously cheap $50/month for what in your case would be nearly unlimited iterations of virtual machine backups. I don't work for Carbonite but this is a super deal so I thought I'd share.
Don't mean to pour any water on your fever for Carbonite, but have you calculated how long it will take to upload 100gb of data to Carbonite through your internet connection? Before moving to the cloud for backups, you need to test it thoroughly. It doesn't make any sense to put your backups on the cloud if you cannot make them in the duration known as the "backup window". While the true measure of any backup is how fast you can recover your data, if you can't complete the backup to begin with, you have a much bigger problem.