I got the Mackie Big Knob Passive for a coworker. It's around $70US. It allows you to switch between two sets of inputs and two sets of monitors. It comes with a mute and a dim switch. It'll last forever since it's passive.
Your other option is to buy an inexpensive four channel compact mixer to be the gate-keeper to your monitors. A four channel, stereo output mixer is $60US. That will come with more routing options like control room vs main outs.