Hi @jakub, USB stick (https://z-wave.me/uzb/) could be the way. There's difference in GPIO shield and USB stick. GPIO shield includes software licence. Anyway, you probably can use opensource OpenZWave (http://www.openzwave.net/, https://github.com/OpenZWave/open-zwave) like free alternative.
It's result of my Z-wave exploration. I haven't used this yet, because a use Zigbee with my UniPi.