It's probably the difference in looking at weight versus calories. A cauliflower is, on average, 0.7-0.9 kg (1.5-2 pounds) and provides about 25 calories. A McDonalds burger is, on average, 0.2 kg (0.441 pounds) with about 250 calories. The cauliflower currently costs about 3 euros (yes, you read that right) in the Netherlands while a burger costs around 7 euros. So, calories per euro is 8 for the cauliflower and 35 for the burger.