[Don Plumley]

In the DOS days we did this with an add-in board that had four monitor+keyboard and ports and software that would run four simultaneous sessions.

The problem is you are thinking of a minicomputer scenario (central CPU and dumb terminals) in a cheap PC world. But unless you were running TTY terminals, the cable length for a monitor/keyboard terminal into a host board becomes an issue.

So the simple solution is to buy four cheap PC's with a small CPU box, then use a router on the network cable.