In true form, the right price for any given playtest card is simply whatever someone is willing to pay for it. Judging by eBay listings, that price is anything but consistent
You see, Blasphemous Act actually costs one fewer generic mana for each creature on the battlefield
Overlord of the Balemurk (Japan Showcase, Fracture Foil) $133.02 Overlord of the Balemurk isn't the most exciting among all of the Overlords, especially since its effect only lets you fish out creatures or Planeswalkers from your graveyard back to your deck
Collider has revealed four of them, while The Darkness Crystal was revealed back at PAX East
It is also a great punishment for anyone using lots of treasures, clues and other artifact tokens
Maximum interaction (which means cards that are hard to interact with are more likely to be cut, so no planeswalkers, limited shroud, only temporary spells/abilities give unblockable effect)