LetsEncrypt offers free SSL certificates, if you’re familiar with reverse proxies then it’s not too difficult to implement. I have mine set up to automatically renew my wildcard cert, then send a special signal to the nginx docker container for it to reload the SSL certs
A more onedrive/google drive-like alternative to Nextcloud would be Syncthing, which is E2EE and doesn’t need additional config of SSL certs and the like