Hi,
SAKAPO is a service I've written some years ago to keep an eye on certain Amazon articles. As with all my tools it started out as a "for my use" only and became public at some point. It's very rudimentary and there are a lot of these price watchers out there (by now anyway).
But if you're interested, I could make tweak it to give it an additional English UI.
You basically add the ASIN of an Amazon article (ASIN = Amazon Standard Identification Number) to the watch list, enter your price limit (you have to use the "," as delimiter for now) and it'll inform you when Amazon drops the price to or below that limit.
If you want to check it out, the address is
http://sakapo.deSimple German crash course:
Registrieren = Register
Benutzername = Username
Anmelden = Log-In
Überprüfen = Check
Bestätigen = Confirm
Hinzufügen = Add
Bearbeiten = Edit
Löschen = Remove
Übersicht = Overview
Einstellungen = Settings