Resistance of a material during dielectric breakdown?
If you download this thesis pdf, at page 22 you will see the resistance curve of a typical arc (5kV, 30kA), it's (>0.5Ω)→0.15Ω according to the paper. I believe the gas is air. Found it on google, 3rd link.

Here's the figure I'm referring to:



Later at around page 52 there's a couple of more similar graphs for different pressures. But the figure above matches the air figure at page 53.