Check Amazon for the "Old Smokey" thermometer, its $10. I used the 2" which allows the movement of grill past it.
Yes, expanded metal.The 2" probe is able to closely match the temp probe I drop thru the vent, so I'd say works well. Are you planning to make a charcoal ring from expanded metal? My is 4" tall and the same diameter as the charcoal grate. Tried and true.