Modern hdmi (I'd recommend dp versions instead of hdmi) kvm switches aren't very expensive. I'm using a 4 machine hdmi/keyboard/mouse/usb switch that was <$300. They make dual monitor ones too. Tho I just use a cheap hdmi switch for my secondary monitor because it doesn't emulate a connection to the PC while a different input is selected.

This allows me to extend my active desktop to two monitors, or show a different machine on the secondary monitor. I also use barrier for this two host configuration.