Home Made Two-High VESA Monitor Stand
One, measure the size of your monitors to get the vertical spacing.
Two, drill holes big enough for metric "M4" screws on 100mm by 100mm square patterns at positions appropriate to your monitors.
Three, 3" nickel plated hinge into back board and foot.
Four, two strips of wood int 2" strap hinges. The first of those into the back board, the second so that it slides parallel and incontact with the first but with the hinge attached to the foot.
Five, tightly wind string around wood strips to bind them together and adjust tilt of whole setup.
Bonus! Tilt adjustable is nice anyway but it means I don't have to worry about getting the monitors exactly perpendicular to the base.