I traded a freaking Time Walk at a tournament once for a pair of Vesuvian Dopplegangers, Berserk, and a Legends Carrion Ants. Which at the time was actually a solid trade!
I've noticed this too, certain cards that used to cost a lot are now cheap and vice-versa. For example, 4th Carrion Ants was worth a few dollars back in 95, now it's going for around 20 cents.
Is this because they printed a lot of them in later series, because they were banned from play, or just a fickle market?