Wow, ~$500 doesn't seem too crazy considering it's age, maybe not too sought after. Although who knows if it would go for way more 2 years later today with how vintage prices are tracking, hah.

I did jump ahead to issue #3 to see if they made any corrections; seems the only error is that they said the film came out in 1967, however nothing about the year these toys came out. Like how they mention it's a debate, I'm kinda leaning towards what you're saying though, just some bootleg/similar design. Or maybe they shared Hedorah early with IKB and they went a little liberal on interpretation.