Simply put, my personal opinion is that only gozuki and skull can do what they are supposed to do. If you don't have gozuki then skull is a must have. Else this deck can be really inconsistent.
If it feels expensive to you, you may want to invest it since they are staple cards for zombie deck; or buy other deck :)
Ok so I try without skull and with 3 gozukis and it's ok. I replaced 2 skulls with lady vampire, because it's more "bullet" to trigger the field effect and destroy one card
you can also use desire to mill. I use 2 gozuki (though i have 3), and 3 skulls, since its effect triggers when it's banished by onslaught, and one desire