Comparing a pay-per-use data storage service like Amazon AWS’s S3 against a service with maximum reserved storage is a bit of an apples-to-oranges comparison.  If you have, say, 100 gigabytes available through a Sugarsync account, your unused capacity will always be greater than zero.  You will always pay for some amount of unused capacity, making your actual gigabyte-month costs higher than they would be if you were only charged for actual usage.  That said, here are some current costs by gigabyte-month:

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