Quantity of data to backup and the method doesn't directly relate to the number of users.
What is the volume of data to be backed up?
What frequency of backup is adequate for your companies needs?
Do you have SQL or other similar database that needs backed up?
What are the OSes involved?
What kind of recovery time is allowable (minutes, hours, days, weeks)?
What types of disasters are you protecting against (building, site, city, virus, etc)?
Do you need to meet regulations with this solution?
Okay, a couple are probably far fetched for you but there is more thought needed before a reasonable estimation could be given.