How can we do MATIC (Ethereum ⇋ Polygon) cross-chain transfer? Is there any sample script to transfer funds?

You can use polygon bridge to transfer funds.

Here is the script: https://gist.github.com/hukamnonceblox/67566e9c0da8a12d9cef8911e1cc5024.

This script includes deposit and withdrawal functionality. You will need to manually customize the scripts according to your requirements. For example, if you are performing a deposit, you will need to comment out the withdrawal methods, and vice versa for performing a withdrawal. 

Additionally, you can visit the maticjs-fxportal library for more ideas: https://github.com/fx-portal/maticjs-fxportal.