it depends on how much data you need to send and how quickly you need to send it. In fact a wireless doorbell is a good way of doing it if it is suitable. The doorbell maker will probably have sourced all the components in China and you might be able to get the whole package cheaper than buying the individual components. I used a wireless doorbell as a repeater for my house doorbell some years ago. I could never hear the one in the hallway, so rigged up the button push to the relay on the doorbell sounder and put the wireless bell box upstairs. Worked a treat - and cost about $10. I see no reason why you cannot pulse the doorbell button on and off for some crude CW modulation