Ask HN: Is there an Amazon Subscribe and Save monitoring tool out there?

I like Amazon Subscribe & Save, but the bait-and-switch (on price, not product) has bitten me a few times.

You only get alerts from Amazon if the price goes up 15% from one automated purchase to the next. If the price goes up 14% one month and 14% another month, they won't notify you. the notifications aren't great, and I usually miss them.