My guess is $20—$25K on both books, but it's exactly that—a guess. It all depends on who's bidding on a particular day.
D.C. let the character of Plastic Man slip into the public domain, which would have killed profits from tie-in toys, etc., so there was never a major motion picture and never will be one. A streaming-service-era version of a made-for-T.V. movie was released on H.B.O. Max (yawn). I like the character, but comic book speculators don't seem to. Still, if Plastic Man had been featured as the main character on the cover, then it would probably be a $50K book in 8.5.