You have two manufacturers making cheap and easy to use HF
modules: Aurel and Mipot. They use AM or FM waves depending on
the device. the cheaper ones are dedicated to 1 bit digital data
transmissions.
They are presented in the form of a small single in line (SIL) module
a bit like the Basic stamp 1. you just have to plug it on your
application, providing a single power supply, an antenna, and that'it!
you input your signal in TTL levels on the transmitter and get it back
in TTL on the receiver.

An example is the Aurel TX-433-SAW (transmiter) and the corresponding
STD 433 SIL (receiver). Those ones are accorded to each other, have a
range of 50 to 100 meters, and may be more with big aerials.

In France you can get the pair Tx/Rx for about 30US$