You can just use Synergy. It will turn off the display that the keyboard and mouse aren't on, so the monitor will hopefully auto-switch to the other input.
Failing that, most monitors have a serial command interface, so you can just tell the monitor to switch inputs when the keyboard and mouse move to the other display.
You're right though, there are no acceptable DisplayPort KVMs for less than $700.
Failing that, most monitors have a serial command interface, so you can just tell the monitor to switch inputs when the keyboard and mouse move to the other display.
You're right though, there are no acceptable DisplayPort KVMs for less than $700.