Hi, @tharun_p. Our service doesn’t offer any method to limit usage based on the cost of the add-on. At this time, the only way to pay for a single bandwidth add-on packages ($20), would be to watch the bandwidth usage in the web UI and then to disable the site if it is going to use a second bandwidth add-on.
We do have an open feature request to be able to set metered limits by dollar amount and to automatically disable sites or site building if that limit is reached. We will post an update to this topic if that feature becomes available. Again, however, it isn’t possible at this time.
The 100 GB of bandwidth (and technically it isn’t “bandwidth” it is “data transferred”) resets monthly.
So, if you use only 99 GB in a single billing cycle, you won’t be billed. If you use 150 GB, you would be billed for a single bandwidth add-on for 100 GB. Note, unused bandwidth does not roll over to the next billing cycle.
The next billing cycle the used bandwidth will reset to zero and you won’t be billed again unless your sites use more than 100 GB in the next billing cycle as well. On other words, you only pay for extra bandwidth if you actually use it. Each billing cycle includes a 100 GB of bandwidth allowed.
If there are other questions about this, please let us know.