The new Sorin planeswalker is busted! The reason is the minus three ability, which allows you to put any Vampire creature from your hand onto the battlefield right after you play Sorin.
Just like Lotus Field, this card will be exceptional in Modern, and thus the price will increase gradually. It's hard to say how high, but expect it to reach around $20 in the next year or so.
The EDH crowd will love Sorin, too. It can go right into the Edgar Markov deck or create its own mono-black Vampires archetype. All of this will influence the price significantly.