It's not the $20! It's the baby! Getting a baby to hang the motion tracking device on will be an issue. I mean, do you rent it? Adopt it? Make your own? - which means getting a woman...

It's the chicken and egg problem*. If you are pushing a baby in a stroller in a supermarket, women will come up and talk to you. I remember thinking when my kids were babies and I took them to the store "damn, why didn't I have one of these when I was single?"

* the egg came first.