As always with a wireless solution, the critical parameters for selecting a solution are required range and power consumption.
You might be able to identify a cheaper pair of sensors, or even find a MCU which is integrated with the sensors you need (and a radio) if you're lucky.
The sensors you found seem to simply broadcast digital data continuously, so whilst you could connect one of these to a 433 MHz transmitter, you will only get one channel.
A more standard approach would be to use a Wifi/BLE/ZigBee/ah-hoc wireless module which exposes a limited amount of spare processing power, and use the wireless module to control when to send data samples. These modules come in at $2-3 (wifi seems cheaper than BLE) and ought to be suitable for battery power applications. You will of course need to learn a new software/toolchain approach, but with luck your endpoint application is a simple example which you can just import with minimal modification.
Once you accept an MCU into your endpoint, you can use any sensor, using a 'single pin self timed', SPI/I2C digital interface, or even an analogue input if you find a device with a spare ADC input. In fact, there is a wide range of options which will allow you to try and compete with this pre-built ESP8266 implementation, but you will struggle to come in at better than the sort of prices that Xiomi are achieving. I guess that the device I linked there is 'open' to some extent, but need to wait and see.