I don't usually recommend Chinese radios, but the WLN C1 or Retevis RT22 would work for this and runs about $20. They are essentially the same radio. They are UHF 16 channel radios, and are very small in size. Program the channels as receive only and go for it. They are also fairly durable. The con is that they don't have a screen so you will not see the channel selected if you manually select one of the channels.
To solve this, there is a variant with a small segmented display, the C1 Plus or the RT22s for a few dollars more. The RT22s is claimed to also have 22 channel capacity, I am not sure if the C1 Plus also does.
Again I want to emphasize make sure it is programmed for RECEIVE ONLY.