It depends on the month for me too.  Thankfully I still have that unlimited data plan too.   This month is going to be higher in the 5-6 GB range since my landline internet was out for a week and I used my mobile hotspot to get by.  I have gotten up to 8 or 9 GB, but that was due to an application that was using too much data in the background until I figured out the drain.

For other months, it ranges between 2-3 GB.