Updox charges a base fee for 3 users, plus a charge for faxes over 500 a month. They charge nothing for emails. It is simple to configure a conversion program (we use Fax Talk; others use Snappy Fax) to automatically convert all of the incoming faxes to emails. You never even know this is happening...until you get your monthly bill from Updox which shows roughly zero faxes for the month.
The Updox people are fine with this.
Your 2000+ faxes each month would still be covered by your base monthly rate.