Why is the cost of diapers such a big deal?

Me and my husband are on a really tight budget (about 200 a month) and when you are trying to make ends meet that $40+ a month really adds up. That could be $40 you spent on gas so you could go out and find a job, money to keep your phone on, money to pay insurance or anything. That $40 really adds up too. In just 2 years you would have spent a minimum of $960 on just cheap diapers. That really adds up. Not to mention that 2 years ago you could have bought a small cheap pack of diapers for $5 and now the cheapist pack is $7