What about adrive.com?
Just stumbled upon them (they seem to be typo-TLD-squatting on rsync.com), and noticed that they advertise "unlimited" storage but with somewhat vague terms (" Please contact sales@adrive.com for a competitive quote."). Their "Business 200GB / 10 Users" is $7/mo.
OTOH they offer WEBDAV, which means they should be immediately usable with rclone.
I'm creating a test account there and will report on what I find, but would be interested in hearing about other experiences with them (on the rclone forum I located only one topic from almost 5 years ago, where an issue was found and a support ticket was created (@ncw, how did that go?), so it doesn't seem to be a very popular alternative...