Well, its obvious that the ability to at least see three cards deep is worth at least 1 mana (Compulsive Research and Thirst are 1 mana more than the baseline efficiency), but given the strength of these two cards, it is probably worth more
However, the effect is inconsistent since it relies on random milling, making it generally weaker than more reliable enablers like Tome of Aetherwind (card draw), Lesson in Lava (damage plus filtering), or Aether Flarestyle direct damage instants that guarantee output without setup
The common sentence that I hear a lot to describe this is: The card will never do what you want it to do, it will do what your opponent wants it to do. If that statement is true, then why is the card constantly bought from my display case at $1 a copy, and why is it immune to reprints from a value perspective
Stifle-ing the sacrifice trigger stops the creature from being sacrificed, effectively keeping it on the battlefield indefinitely