Monitoring (when pinging every minute):
Upload: 800 Bytes (per ping)
Download: 1100 Bytes (per ping)
Upload: 1.125 Mb (per day)
Download: 1.54 Mb (per day)
For snapshots (approximate based on your current snapshot):
Upload: 100Kb (per snapshot)
Upload: 2.34 Mb (per day)
Total estimate for monitoring and snapshots, in addition to content modifications and publishing of presentation, is 2.34 Mb of data per player per day.
If you need help lowering your data usage please refer to How do I reduce my data usage?