Try out https://dartpm.com/

Someone is trying to create a dart package manager taking inspiration from node package manager.
It is in beta currently, but best part is it is free right now, for private packages as well. Also it doesn't look pricy.

To publish the package (docs)
1. Create account

2. Create org, click organization in user icon dropdown

3. Install dartpm cli tool
dart pub global activate --source hosted --hosted-url "https://dartpm.com" dartpm

4. Login dartpm cli
dartpm login

5. Update pubspec.yaml of a package you want to publish
publish_to: https://dartpm.com/registry/org-name

6. dart pub publish

Also sharing the package is very easy as well.

1. Create a granular token from organization settings.
2. Add package and access.
3. Give the token to anyone to use the packages. Even client don't need to use dartpm account to get access.