You can get 433mhz serial links from ebay, locally or from Asia. Usually found under 433mhz Arduino Radio. Make sure to get TRANSCIEVERS, as some are just receivers or transmitters.
You can some that have this longer antenna. It is better for range but the obvious drawback it needs some more space.
There are also ones with an embedded coil. They work well too. I cant comment on min or max ranges.
The simplicity of this is that its a transparent UART channel so you can add as many transceivers as you like and all the nodes will get the data. You need to create some kind of simple model where you embed an ID, the NODE you are interested in a multi tenant environment, and the command or data. These are fairly cheap and have built in stacks to modulise demodulise the data.
The drawback is security. Anybody can sniff these packets, or inject fake packets. The easy way is to encrypt your model "String" - How storng depends on you. Reuse cryptographic libraries available on each platform. If you going to be sending allot of data then encryption can cause CPU usage issues. And if you plan on building cheap nodes, they might not be able to decrypt the data because of slower MCU's
In my opinion, this is the simplest and cheapest way to do it.