If you want an idea of what you can do with an hcmos inverter on the Txd pin: I ran one 50ft to my desktop pc to get some data (was not designed into product.) No errors, 9600 baud.

RS232 is designed for more than noise immunity, it is spec'd for distance and speed, and current. So to say you need rs232 for a short distance is overkill.

But, you should consider noise immunity relative to your environment. Using a 74hC14 would be a good compromise.