We don't generally "like" shopping questions on these websites so you won't get many of the "try these people" kind of answers, but we're happy to help you figure out what's important to you to help you make the right choice yourself.
To that end, I'm going to hit you with the questions I always ask myself / other people when planning a backup system.
If you think backups can be expensive, you ought to try losing all your data. That's expensive
You might start by defining what, exactly, backup means to you. Do you need to backup databases? Email systems? or just a bunch of files? Will the machines being backed up be on all the time? Connected to the Internet all the time?
You also need to define "affordable": do you just want something cheap on the "anything's better than nothing" basis, or have you actually sat down and worked out how much the loss of some or all of your data would cost you and have a budget based on reasonable costs of mitigating that risk?
If you think backing up is complicated, you ought to try restoring
Do you expect to be able to do a "bare metal" restore of your systems, including OS and data? Or just install the OS yourself and copy the data back?
How long is acceptable to be without data in the event of a loss? Will your Internet connection support upload and download times that will give you enough performance to meet that level of acceptability?
What happens if Fred sets this backup service up then leaves the business?
What happens if Fred doesn't leave the business, but goes on holiday and everyone else forgets the password to the site because Fred does all the "management" of the backups?
Will this be your only backup of the data? Or is this an additional backup on top of the NAS, say?
FWIW, I use crashplan to backup several machines as a home user rather than a business and I'm very happy with them, but I'm not so sure they do backups of NAS devices, and its not something I saw offered by anyone when I was looking around.