Mining consumes very little bandwidth.
Running a bitcoin P2P node consumes a noticeable amount of bandwidth -- my VPS ran out of its 1000GB allocation this month.
Wow, do you mean your bitcoin client communicated a terabyte in a month??? That doesn't sound right.
Average block size is about 3.5 kB, that makes about 15 MB/month. If you had 100 peers that could be maybe 2 GB/month.