Zigbee is doable. It all begins with NordicSemi’s nRF52 series of microcontrollers. These microcontrollers feature an 802.15.4 radio. Nordic further more provides an SDK for Zigbee and Thread which is based on ZBOSS. It’s relatively easy to develop a device based on this platform - provided you are an experienced firmware developer that knows his/her way around C.
The nRF52840 is the workhorse of the nRF52 family. It costs ca. €3 in 1k+ quantities, so it’s not a really expensive chip. There’s a full size development board available for ca. €40 and a much smaller dongle for ca. €9.
One of the best things in the NordicSemi ecosystem is the availability of the excellent SEGGER Embedded Studio toolchain which is free for use with the nRF52. Since the nRF52840-DK provides an on-board SEGGER J-Link compatible debug probe, the total development environment is very, very affordable.
