Here is a simple patch which, when you click the "save prices" button, checks if there is an item which you priced at more than 100k meat but less than 10% of the cheapest in mall. This way, the check is done only for items whose mall value is 1m meat or more.
When there is one such item, a pop will ask you if you wish to continue. If you say no, the new prices won't be submitted. You will then be able to correct the price and use the "save prices" button again.
If you continue, you item will become the cheapest in the mall, and Mafia shouldn't warn you again.
I'll let Hola or Veracity go over my patch before committing it.