For the data usage, it depends on the bitrate you set up for the camera. The default bitrate is 1.5Mbps(for the mainstream, up to2Mbps)/160kbps(for the substream, up to 512kbps).
You could find the settings refer to the picture below:
With the default settings, if the mainstream is previewed, about 1 minute per day (if converted into substreams is about 12-15 minutes per day), you need 1GB monthly.
Please kindly note that it is just for reference, the actual cost is based on the actual working situation.