I have a Dell laptop for work - model E6320. I use the laptop screen in a dock and a Dell monitor so I have dual screens via the display settings.
In the same room, I also have a Gateway PC with an HP monitor for personal use.
I use Microsoft Garage Mouse Without Borders to switch between laptop/Dell monitors and the PC Monitor.
I'd like to eliminate the laptop screen and use the Dell monitor and the HP monitor (dual screens) and be able to switch between the Dell laptop and the Gateway PC all while using the same keyboard and mouse.
What is the least expensive but efficient way to make this possible?

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