Silvally

Silvally was once the cheapest DT card, until the Kalos update came along. Silvally is an upgraded version of Type: Null that, instead of putting a Legendary rarity Pokemon into your hand when it dies, puts a Determination rarity Pokemon into your hand! This means you can get powerful cards such as Hoopa or Pheromosa. It costs 300, though. You can use Cost Lowerer to lower its cost by 20, or you can just buy the special update and put it out without any trouble.