Inexpensive Cloud based solution for file sharing with users login/password and usage tracking recommendations?

Hello,

I’m looking for a solution to build an extranet to share files and documentation:
- Cloud based
- With users login/password manager  (I create accounts, emails,  passwords)
- With usage tracking (who downloaded/read what, when)
- User can reset his password himself
- Inexpensive and not priced by authenticated user
If it has site builder it is even better!

I'm confused among all the available solutions.
Any recommendations?