I have a 10 week old and we've kept meticulous logs of diaper changes[1] (and everything else). We get 12 diaper change days a couple times per week. 9 is more typical. $1000/yr is pretty high but not unbelievable. A lot of grocery stores and small shops don't sell diapers in cost saving bulk packages so it really just depends on where you live and your access to more economical options.

1. https://i.imgur.com/IAFAu18.png