This seems like a cool idea, but in my experience Amazon's prices for household goods fluctuate dramatically. Sometimes things are a great deal, but a month later they could be more expensive than purchasing at a local store (and I'm in NYC, the stores I'm comparing them to certainly aren't cheap).

So I'd be willing to use a button like this for a store with consistently low prices like Costco (or even WalMart), but not for Amazon.