My apologies I should have informed you about this tool earlier. It has been in the Store now for a number of days. If you are a user of Windows Phone this App is right in your alley. WP Market Deals is exactly what is says, shows you apps dynamics in Windows Phone Marketplace, Apps that have gone Free, or lowered in Price. Keeps you up to date with high-profile apps for which price have temporarily reduced by Vendor so the app can gain popularity. The following is the description of the App by LuviSoft in the Store:

Description:
Find out about the best deals on the Windows Phone Marketplace, and get your favorite apps at a discounted price.

Features:
Automatically shows new deals when they are available
Filter apps by popular (most downloaded), top rated, apps gone free, Xbox Live (Deal of the Week),
Share deals

Download this tool for your Windows Phone via this link: http://apps.microsoft.com/webpdp/app/31a0584a-626c-4d02-a5bb-45bdb86c0836