Cheapest radio RX, TX

What is the cheapest way to send a very basic on/off signal over radio? Basically like wireless doorbell style, just some sort of high signal when a remote button is pushed. Range isn't a big deal but further is better obviously. I'm really only worried about within a room.

So far the only things I can think of is either tearing apart a wireless doorbell($10) or using a couple of transceivers(or transmitter and receiver) intended for serial communication which is overkill but actually cheaper than the doorbell(like $3 per transceiver).

Can I get cheaper than this? I'd like to stay simple but beggars can't be choosers. I wouldn't mind building the circuit myself.

Just looking for any info on the matter to get a better idea of my options. Thanks.

 

Wireless doorbell option will be the cheapest in terms of parts (components, board and box). It will also be the easiest technically.

With an old garage door opener, you could even get security.

Another option might be infrared like a TV remote control. This will be a simpler circuit to design but, again, the wireless doorbell hack will be easiest. Once you open the box, you will be on your own since nobody will have a circuit drawing to help you if you cannot easily find the core of the receiver/actuator you need. The transmitter button will not need any work