There was a 50% off coupon code for https://www.interserver.net/vps/storage.html that brought it down from $6/month to $3/month. Not sure if the code is still active or if it works for larger plans.
zfs send/recv support? That seems to be the missing piece in the low-end cloud storage world. There's rsync.net and zfs.rent, but those seem to be targeting 10+ TiB. (My current solution is a 1 TiB 'storage' VPS for $3/month, running Debian ZFS on root. Works nicely, but scrubbing 600 GiB takes over a day!)
I'm not sure a one week trial is long enough, considering you're asking for annual payment up front. For instance, I didn't want to 'start the clock' by creating an account.
Borgbase has a 2 repo / 10 GB free tier, and lots of object storage services offer 20-75 GB free.