Price and Stock data in absolute realtime

I'd like to give a list of # to ## websites that list certain items for sale and be able to check these sites every ?? seconds for item availability and price and be alerted if certain thresholds are met. Via sound, email, SMS, or other if needed. Item in stock and price met criteria is critical and needs to be alerted ASAP. Project must be locally hosted on my machines/servers and written in PHP, MySql. Javascript and Jquery is ok if needed.