Agreed, generally between a more base limited package and the lowest unlimited, is only $10ish usually.
One thing you may want to look at though, if the usage trends continue, is to track down WHAT might be using that usage?
Is there a computer that is stuck on windows updates, and just keeps retrying them?
Could go further, that its something malicious, a virus/malware, which is being used as a host for something bad sending/receiving data without you knowing.
