For BF'ing "I'm too cheap to buy formula" Or "it saves on milk/juice"
For co-sleeping "it's cheaper than an electric blanket - not to mention more environmentally friendly"
For siblings "Oh I hate my siblings, I wouldn't want to inflict that on DS/DD"
for haircuts - "We're waiting till he has enough hair so we can give it to a charity that makes wigs for cancer sufferers"