[Walmart] Fitbit Flex (first gen) $29
This is the most basic model of the fitbit. Only does step count and sleep track.
At this price, you can get the xiaomi band2 for much better battery life and more robust features.
But the fitbit ecoystem is probably the best out there. Their app is much better thatn xiaomi's and if you have friends/family/co-workers on the fitbit system, following them onto the fitbit ecosystem would probably yield better benefits due to the competition and such.
So with that in mind, this is a great price to join into fitbit if you just want to track your steps.
If you don't need motivation from peers to do your daily exercise, then consider the xiaomi instead.