[SpiderOak] offered one of the first GNU/Linux clients.
They have decent pricing, zero knowledge e2e encryption. Only issue, really, is that their servers are in the US. Otherwise they’re good and you’ll probably be alright unless you’re potentially a target in which case you need to be self-hosting off shore.
MEGA* is another good provider. They’re based out of New Zealand**. Also offer e2ee but also released the source code. It’s fairly fast and offers more bundled in stuff like chat and contacts.
Both allow you to share files and keep select directories synchronized. There’s a bunch more I could write but just take a look at their websites yourself.
I just found out about BackBlaze. Super cheap, allows you to use your own encryption key and uses Duplicity under GNU/Linux. Hosted in the US (and/or Amsterdam?), closed source but, does boast about physical security practices in the datacenter.
Then, there’s SyncThing which is an open source bittorrent protocol based service you run on your own machines. It’s really cool and I’ve heard great things recently but I haven’t played with it yet.
Another option is to find a good object storage (s3 compatible) provider that you feel comfortable with that’s within your budget and set something up with that. You’d pay “only” for what you use as far as data and bandwidth goes.
(Use promo code TWIT or visit twit.tv’s sponsors page if you settle on Wasabi – cheapest one I’ve found so far.)
If you want to just want to sign up to some Nextcloud provider there’s disroot.org and many listed here: github com/nextcloud/providers#providers which is far from an exhaustive list.
I’d recommend not using ProtonDrive as it’s in beta and you’re required to pay for a mid/higher tier of other services in order to access it. Plus, I’ve heard some bad things about them.
If you’re in no hurry, eventually Purism will be rolling out some form of cloud storage called “Librem Backup” and “Librem Files” as part of the Librem One services package. I don’t know anything about what it’ll be but I’m curious.
_* Please use my referral code if you sign up so I can get a discount and stuff. lol I don’t think any info is shared – just use a unique alias/screen name if you’re concerned.
** Part of the 14 eyes but generally says 
whenever possible and has very, very few legitimate, actionable DMCA takedown requests.
P.S. No, WD cloud crap doesn’t work on any OS other than windoze and maybe fruitOS.
And remember, “the cloud is not a backup!”
P.P.S. Sorry for the lack of links. I just had to remove a bunch because I’m a “new user” who’s been subscribed to L1 for probably over a year now. 
Frankly, I still suggest
