User Exit in MR21 Transaction

Hi,

I am trying to execute the transaction MR21 (Price change).

I entered posting date, company code, Plant in the first screen of MR21.

In the second screen I entered Material and New Price and hit Save button.

My requirement is as soon as I hit the save button I need to validate some condition. If the condition fails I have to through an error message to user.

Can anybody help me is there any user exit to do this in this transaction? Or else please suggest me some alternative way.

Thanks and Regards,

Suresh