If you are are willing to forego a LCD display and battery power, the most cost effective and accurate solution is to buy a Ecowitt GW1000 (~$30 USD )and stick the probe end in the freezer.
You will have live temperature data on your phone (WSview app) and can set an email alert on ecowitt.net. (You can view live data and charts online even if you are out of WIFI range or far away from home) BONUS! You will have humidity and barometric pressure too!
The GW1000 needs power from a USB port. Any old phone, tablet USB charger should work.
One caveat. The GW1000 sometimes does not like to be plugged directly into a USB charger power supply (the power supply might interfere with WIFI). You can fix this by getting a short USB extension.
This equipment is available on amazon.com.
EDIT: Sorry, made an error! In double checking the GW1000, it can measure only down to 14F/ Freezers are usually set to around 0F. There might be other remote sensors. More research required.
Ok. An Ecowitt WN30 ($17 USD)will work.
Specs: Power: 2 AA batteries(not included)
Sensor Size: (LxHxW): 4.75 x 1.5 x 0.6 in (123x 42 x 14 mm)
Cable Length: 3M(10FT)
Frequency: 433 / 868 / 915 MHz depending on location (North American: 915 MHz; Europe: 433MHz; Other areas: 433MHz)
Temperature range: -40°C – 60°C (40°F - 140°F)
Temperature resolution: 0.1°C, or 0.1°F
Temperature accuracy: ± 1°C /± 2°F
Waterproof Level for the probe: IP65
Sensor reporting interval: 61 seconds
Unfortunately this probe is not available on amazon but could be ordered from ecowitt.com.
Sorry for the confusion!