The all in ones are more expensive up front but it's worth it in a couple of months.
My sister-in-law and I, had it figured that the plain old-fashioned method of diapering that we used in our homes had already paid for itself (once over) within the first month of use.
1980's prices (from what I remember approx.)
Cotton flannelette diapers - .74¢ a diaper (dozen to a pack) - $8.88
Diaper pins - .25¢ per pin (4 pins to a pack) - $1.00
Rubber pants- .24¢ per pair (6 pairs to a pack) - $1.44
Plastic diaper pail - second-hand (passed-down to me from family)
With my oldest, I started off with 3 dozen diapers, a few sets of pins, and a dozen pairs of rubber pants. Total cost, $31.02
When baby #2 was due, I bought 2 dozen more diapers. Total cost, $17.76
Those 5 dozen diapers covered the entire diapering needs of both babies (newborn to toilet training), then went on to diaper the bottom of baby #3. The only expense I was faced with related to the old, was rubber pants and laundering, which equated to nothing more than pennies per pair (rubber pants), and pennies per wash-load (laundering).