I bought a Xiaomi Mijia Bluetooth Temperature Humidity Sensor at Tmall.com. The price is RMB 67.90, converting to CAD$13.56. No tax added.
It has a LCD screen. Powered by one AAA battery.
Let’s look at the specification.
Here are some pictures I took when I open the package and install it.
The left upper item is base. There is a sticker at the back. So you can stick it on the wall. The base is attached with a magnet which can hold sensor body.