An infrared thermometer able to measure as high a temp as the runners will get too is likely more expensive than 4 EGT sensors. The $100 guns you find at most places definitely won't read that hot, or they never used to.

What gun/thermometer do you propose using?

I'm with Mike - just throw in an EGT sensor on each runner. Or if you wanna do it on the cheap then use one EGT sensor and switch it between runners although this would be incredibly inefficient and time consuming. If anything just buy 4 sensors and one or two gauges. Heck, you can find them used for next to nothing.