3C273 jet mass estimate
Trigger Warning:  Major hacking going on here.
[edited from 1 ly to 1000 ly diameter]
Scaling from the image, I'll approximate the jet diameter as 1000 ly . So there's a volume of roughly 2e4*1e6 * pi/4 cubic ly.   For absolutely no good reason, I'll propose an electron ejection density of 1E6 per cubic km -- at least those are round numbers and easily scalable if anyone can find references to actual calculations/measurements --, so using 1 cubic ly = 8.468e+38 cubic km, I get 1.33e+56 electrons in the jet.