[PeterisP]

We needed a large highly isolating cage for a project and the cost-effective (but still costly) way to do that was to build our own, having local welders make a custom steel box and lining it up with rf anechoic pyramid foam, otherwise the reflections make weird RF noise. A tricky part is the seams where your doors meet the box. It's easier to get good isolation from outside if you don't have to connect any wires, i.e. if any "control" you need is done by a battery-powered computer (laptop or smartphone) inside the isolation.