It is well worth considering the Si4432 based FSK tranceivers. These can be bought for about £1.50 each. They are packetised data devices.
On of the issues with the simple UHF trancievers is that a lot of them are on a few limited frequencies. So interferance from other devices can be an issue. With the Si4432 you can choose the frequency of operation and thus avoid local interferance.
An Si4432 will put out as much as 100mW, but you can scale it back to comply with local regulations, 10mW in a lot of places, including the UK.
You will have a comms link that has far more range than you may ever need, a 10mW Si4432 setup will do around 12kM LOS on simple 1/4 wires, but the advantage in your case of this type of capability it that for short range use you dont need to worry too much about antennas.