The described project is for one-way or two-way communication using (i. e. transciever). If you know you will only send commands "blindly" you can attach a transmitter to the PC end and a receiver to the Arduino. Those modules are really cheap.
Step 1: What you need
- USB serial adapter
- Two or more Wireless RS232 modules (e. g. EWRF 3022)
- Arduino. It's a Nano in the picture but any model should due.
- A gadget box
- Soldering equipment
- Basic Arduino skills
Step 2: Attach the USB module to the transciever
Step 3: Fit the modules in the box
Step 4: Attach the second transciever to the Arduino
Step 5: Load the software
If you want to write your own interaction you may want to check my CmdCallBack library out. The library makes it easy to link commands with parameter with callback functions in the sketch. I might make a separate Instructable about that.