The $4.99 per month plan, Backupify Pro 100, allows for 5 users on an Apps domain and 20GB of storage. That plan is geared towards small mom & pop operations, not the bigdog system e1ven was running.

Our Pro 500 plan is $19.99 per month and includes 10 Google Apps users and unlimited storage. That actually breaks down to less than $2 per user per month. Beyond that first ten, additional users are $3 per user per month. I usually just quote the $3 figure for simplicity's sake, especially since most admins using a paid Google Apps domain (Google Apps Premium) have more than 10 users anyway.