Last I heard it was 25% of all comic packs (IG/Destro).
So 1 out of every 4. Not exactly rare, but not exactly easy to find either. I think this variant just isn't that big with fans. I love it personally, but overall it isn't a mistake like Yellow Stalker, or a small production run like the exclusives. So that leaves it being less desireable than others.
I would bet a year from now it will be higher in value than it currently is, but it will never get to the same level as Yellow Stalker, SDCC Destro or Rowdy Roddy Piper.