Are you still looking for a low-cost thermometer? Did you get one? Aha! Here it is! This EASY Plug analog temperature sensor is based on a thermistor. The resistance varies with surrounding temperature change.
It can measure temperature change in the surroundings and send the data to Arduino analog IO. Just need to convert the output data to degrees Celsius temperature by simple programming.
The sensor is convenient and cost effective, widely applied to gardening, home alarm system and other devices.
This module should be used together with EASY plug control board.