Disposable diapers just for once child per month can cost from $50.00 to $100.00 per month depending on the brand of diapers you use.
Some cheaper brands such as Parents Choice Diapers may only cost you $50.00 to $60.00 per month while other brands such as Huggies or Pampers can cost as high as $80.00 to $100.00 per month.
One box of Huggies can cost $40.00 and you may need around 2 boxes of the diapers per month and may not go through all of them but you should budget at least $80.00 per month for diapers just to be safe and not run out of diapers.