lololol- I've replaced the sky screens a couple times once on my first chronograph in 1977, then again in 84 with my second one - but that's it. Screens are indeed cheaper than a machine. I'm now using a chrony, where in the body sits downrange with screens - and the countdr box on te bench. So far, it is unscathed, however there is a 1/2 rod nick out of one from a .17 cal. bullet running 3,900fps+.
It does pay, or rather, it costs less to sight in the rifle BEFORE chronographing it.