Have been meaning to drop in this little pearl for a while!
The Institute of Family Studies in Melbourne Australia from time to time
produce figures for the cost of raising children
Recently I saw a figure of A$33.51 (cents may be wrong!) per week cited as
the cost of food for babies under 12 months.
A$1=US$0.72 approximately just now.
For comparison, the maximum rate of child benefits paid by the Social
Security system for low income/welfare recipients is A$46.50 per child per
week.
Seems like a good enough reason for breastfeeding without all the others.

Also pleased to see the comments about individual differences in the timing
of the return of menses & the relative consistency within a single
individual which has been my experience.  I know we can't argue from our
own experiences but my friend did not experience the return of her periods
until the baby was weaned (her "best effort" was no periods despite the
fact that she was only feeding her almost four-year-old one side once a
day) while mine returned as soon as a taste of any other food crossed their
little lips.  Seemed to me unfair!

Dot Newbold