Going through spiceworks the other day, and came across an online backup solution called egnyte. In the little advertisement, it stated unlimited backup. There is one caveat though, which is that there needs to be a minimum of 3 power users added to get it for free. It brings the price up to $45 a month. One other option is to use only one power user and add the unlimited storage for a total of $35 a month. Sounds like a pretty good deal to me, and as long as your data is encrypted, it should be safe.
There is a nice little calculator too.