A hacksaw, a half round metal file and wet & dry paper are all you need really. You'll want to scribe the outline, and you could sharpen the tip of a large nail to do that (using your half round file)
You'll need a couple of drill bits too, as you'll need holes for your pots & switches, and for the fixing holes. Use your largest drill bit as a countersink for the fixing holes. Again you can use your sharpened nail as a centre punch before drilling to stop the drill bit wandering
Those tools would probably cost less than £20