Free for the first time in the app store. HD version too. We likely all played it but you can't beat the price for another platform. I don't know how long this is supposed to last.
It's a buildup for Plant vs Zombies 2, it will last as long as it generates some hype, then they will switch it back. But don't worry, they will put it back free at least one more time prior to the official PvZ2 launch date announcement.