We used a Type K thermocouple set-up in the past with a Fluke gun. The thermocouple and wand were as much as the gun it connected to. I forget the brand we use now, but much cheaper. Rather than paying to have it calibrated annually, toss it and buy another one.
For what it's worth, we aren't allowed to use infrared guns for heat treating purposes. I don't know if an infrared gun can be calibrated or not. Even the stop watches used have to be calibrated annually.
These same engineers (materials engineers) have stated for the record cast iron is a non-weldable material. I'm sure it's for liability purposes, but there it is.