Purchase Order Authorization Rule

I have a user “X” which has rights to submit the purchase order now I want to define one more user “Y” who will submit the purchase order only if the total purchase order values exceeds 10,000 but I want that user “Y” will only be able to authorize the purchase order if the total value of the purchase order exceeds 10,000 INR, otherwise the user “Y” should not be able to submit the purchase order.

Thats not possible without a custom script.

Can you give me one line of example for writing custom script for this scenario.

See this example: