user exit problem(urgent)

hi abapers,

i have a problem in user exit, my client want the tcode me11 material specific, in tcode mm02 he want to give the maximum value (commercial price 15rs.) at the time of creating info records(using me11 tcode) if an end user enter a value greater then the value of commercial price then they want a error message will appear for this condition ( entered value is grater then commercial price) and he don't want this report vendor specific.

thnks

pardeep