Look at the bottom of the bowl before you mix. That pool of oil, chicken fat and kecap is where 100 of the 450 calories live. The seller ladles it in first, then the noodles, then the chicken. It is what makes cheap mie ayam taste good and it is why a bowl with barely 50g of chicken still has 20g of fat.
The noodles are about 150g cooked, around 210 calories, which is actually less than a plate of rice. The chicken topping is 50g of thigh meat cooked down in kecap manis and more oil, about 110 calories. The sawi is 10. So a plain bowl without extras is really 450, and Rp 12,000 to 18,000 at most carts.
Then the extras. Two bakso add about 110 calories. Pangsit rebus (boiled wonton) is 30 each. Pangsit goreng is 60 to 70 each and people take three. Ceker (chicken feet) are about 50 for two. A 'mie ayam bakso pangsit komplit' is 650 to 700 calories and still only about 30g protein.
The broth on the side is nearly free at 20 calories, unless the seller has floated chicken oil on it. Drink it if it is clear, skip it if it has a yellow film.