Ideally, I would like to have my laptops' lids closed and still fully operate them (e.g. video, audio, navigation etc), would that be possible?
Make up your mind, original post says control both from one which implies one has its screen open ... for which you were given various free software solutions, (which you haven't bothered to try).
Now you want both laptop screens closed, for which the only way you're going to get a cheap solution is if someone gives you: a KVM, a monitor, a keyboard, a mouse, and a USB hub.
Get off your butt, go down the Op Shops, (charity shops), and you'll probably find everything except the KVM.