Did you calculate based on buying cloth nappies second hand and then reselling them? That was a great alternative for my family. Worked out to something like $100 in total nappy costs for one child, including the opportunity cost of tying up the capital up front. That's less than $1 per week. Make it $1.5 if we include electricity and water costs of laundry, compounded over that period.

I would struggle to find single-use nappies for $1.5 per week in my area.