As Jon (JBS) pointed out several times, for high volume faxing you can use your own fax line and import them into UpDox without having to buy bundles.
Bert and I use Mainpine fax boards which are also ideal for high volume faxing. I get 1500-2000 faxes/month (from 3 pages up to 50 pages per fax). Doesn't require any software for the conversion as the PDF conversion is built into the driver. You can also fax from all computers.