I think the single button with no screen is actually kind of a nice idea. you buy a few, put them in strategic places (sponge button by the sink, paper towel button by the paper towels, etc), and just hit the button when you're running low on something.

the main deal breaker with the current setup is that the price might shoot up unexpectedly, but this could be fixed with the ability to set a price limit when you configure the device (eg, don't spend more than $5 on a pack of paper towels).