Maybe plexiglas? I know it's transparent, but you can sand it and spray paint? With the right paint you might enven match the colour of the AEM.
Still solid enough for front panel and easy to cut with a thin saw (metal saw or wire saw)
Aluminum sheet, but that may be expensive quickly.
Metal sheet is also a good choice. If you find a place where they only sell metal bars and sheet, they might be able to cut the directly for you at the size you want. You can also look at metal work school, they can do such thing quiet cheap.
I was also thinking acrylic or PVC. It shouldn't be too difficult to find acrylic plates thin enough in a hobby or model shop. It's actually not that hard to drill, you mostly need to go slow, use sharp bits and a piece of wood behind.
I think for DIY without machinery acrylic should work fine; it's available also in 1,5mm like the original AE frontpanels. Other plastic materials like PVC, Styrene etc. are too weak IMO. In a very early phase of AE I was thinking about acrylics as an advanced frontpanels option, my idea was to use a "milky", semitransparent one and place LEDs on the PCB to light them in different colors... 😲