Is there any option for Mongo lite version for replication?

We wanted to use MongoDB as a primary database, which would be common hosting (priymary db) for all-region.
Now, we have region-wise modules depoyment which are independent. And we also need to fetch data of MongoDB in region. Replication is one option, but that increases a cost.

Few questions :

  1. Do we have a ligher option for replication?
  2. How much memory do we need for replication setup in case of worst-case scenario?
  3. Can we set up any other caching instance as replication along with primary MongoDB?
  4. any other suggestion or solution?