Hello,
An interesting issue indeed - something I'd love to get a chance to work on.
IMO, an individual plugin or a set of plugins is not likely to be causing bandwidth utilization or drain, unless the function of the plugin involves fetching/sending live data from/to external resources.
In any case, I'll try and do what I can to lower the bandwidth utilization of your site. Some options I'll try to deploy would be:
1. Enabling gzip/compression
2. Image size reduction and possibly, deployment of a free CDN
3. CSS minification
4. Making more efficient use of 'expires' headers
etc.
I'll be happy to discuss this further if you open a Freelancer chat/messaging session with me.
With best regards,
Richa Varma
BE(IT), MBA (Marketing)
Freelancing Web Dev/Tech WAHM