Popup message for price revision

Hi,

For our business some customers to give the price revision for their product every 3 months once. Some times we forget to change the price and create the sales orders for existing price. So again we create debit memo or supplementary invoice for the price change. In future to avoid this we need the option for popup message to change the price every 3 months once for particular customers only. Please help us in this regard.

Regards,

Sundar