Something worth noting, which is actually something I just discovered, you can chose what item you get from the machine. When you put in 100 yen, you get a random item, but the machine will tell you what the actual cost of that item was.
As an example, I put 100 yen in, and gave me the slug sushi. The machine was then showing a price of 124 yen, so I put in exactly that amount, and got the same item. I did it again, same result. Then again, and again, and again. So I was able to become rotten pretty quickly.
I will note, I had to reload the game once, and it seems the price of the item is randomized each game load. Even so, it makes it much easier to control what you eat. So long as the item isn't 6000 yen.