I have an eQuip KVMA switch for sale. It can switch a single mouse, keyboard, monitor, speaker and microphone between 4 computers. It is complete with 4 sets of cables. In perfect condition.

It is for PS2 keyboard and mouse, but it works with a USB to PS2 adapter on most motherboards.

To switch you just hit the Ctrl key twice and press the computer number. I use one on my own setup. This one was my daughter's. She now uses a laptop on wireless and a single Hackintosh, so this one is superfluous.

KVM switches are EXPENSIVE, running into hundreds of Euros and getting one that supports Audio input and output is neither easy nor cheap. I'm looking for around 50 Euros plus postage.