What is the most affordable back up for websites?

Hi, I recently purchased back up buddy to make my life easier to migrate a site to a new url.

I have some clients who need some remote destination back up.

I was just looking for some input on the most affordable… basically just to store back ups.

I was looking at Amazon S3… anyone else have any better suggestions… if so… why?

I’m looking for affordability (I will only download them off if there is an issue) as well as security and stability.

Thanks… I’ve google it for a while, but still don’t know the best (easiest, most affordable, most secure) route to take… any help?