Can you explain why you can't achieve this via Define limit ?
As per your example, if you condition amount is more than 30,000, then you will receive an error message.
It can be easily achieve through this settings.
Set only the upper limit as 30,000 for the condition type
Then whenever you will try to enter the amount more than 30,000, system will give you an error message.
If your requirement is different. then please elaborate.