Some of the Azure IoT services offered by Microsoft are free, including SDK packages and access to IoT Edge. In the case of the main resource, the IoT Hub, the cost depends on the number of available messages to be forwarded within 24 hours. There is also a free version, supporting up to 8,000 messages per 24 hours. That should be enough to start integrating with the Azure IoT world. You can find detailed information on the costs at https://azure.microsoft.com/en-us/pricing/details/iot-hub/