N.B. I've been using Arq since it first came out, and love it 100%. I do not, however, backup my music/video with it. That goes on a removable 2TB safe in a fire safe.
That same pricing $0.140 per GB (on S3) is $17.5/month unless I misunderstand S3 pricing.
http://aws.amazon.com/s3/pricing/
https://secure.backblaze.com/buy.htm
Dropbox is more expensive but is syncing as opposed to backup.
(disclosure: I wrote Arq)
It's possible to lose your S3 data too (and then you're in the same situation as BackBlaze losing your data). For example, I once accidentally removed all permissions from files in a bucket with Transmit, including the permissions to read files or set permissions.
I think Arq is great, just playing devil's advocate.
(I'm the author of Arq)