Goi cuon is one of the few street snacks where the number is actually low: 65 to 70 calories per roll, 200 for two with sauce. A sheet of rice paper is about 30 calories, the 20g of bun inside is 20, and a prawn and a slice of boiled pork come to 30. There is no oil anywhere in the roll. The published figures of 49 for a prawn only roll and 67 for a pork and prawn roll match that.
The sauce is where it moves. The peanut hoisin sauce is hoisin, peanut butter, sugar and sometimes coconut milk, about 35 calories for the 20ml a cart gives you, and 90 if a restaurant gives you a full bowl and you finish it. The alternative, nuoc cham with lime, is 15. The difference over four rolls is 150 calories, which is more than two of the rolls.
The comparison people want is with cha gio, the fried version. A cha gio is 130 to 150 calories, double a goi cuon, because it is fried in oil. Four goi cuon is 260 before sauce and makes a real light lunch with 22g of protein. Four cha gio is 540. Most menus put them side by side at the same price.