Discounted "borg accounts" are available for technically proficient users:

$0.008 per GB, per month - 200 GB Minimum

  Free ZFS filesystem snapshots are not included since you'll be doing versioning and retention with borg.
 We will not configure subaccounts, or additional logins, for these borg accounts.
  There is NO borg specific technical support or integration engineering. You're here because you're an expert.
 You must pay annually.

No other costs. No contracts. Unlimited borg repositories. All transfer/bandwidth/usage is free.