What is a good and cheap solution for online backup of over 100Gb, probably growing to 200+ in about a year, and then no doubt more after that.

I am looking for something that can work in the background on a mac. I am using Aperture 3. The cost is the limiting factor. I have thought about an external HDD, but I want my data in another place to keep it safe.

[EDIT:]

We have a winner (for now): I am using BackBlaze since it's cheap enough and unlimited. If it turns out to be not up to the job, or there end up being a better solution I will update again. Thanks for all the suggestions!

What is a good and cheap solution for online backup of over 100Gb, probably growing to 200+ in about a year, and then no doubt more after that.

I am looking for something that can work in the background on a mac. I am using Aperture 3. The cost is the limiting factor. I have thought about an external HDD, but I want my data in another place to keep it safe.