Sunflower

The sunflower costs around 150 sun, they are you're best bet in this game as they are the only plant in the game that can generate sun (Besides Twin Sunflower).

Trivia

 * Unlike PvZ, Sunflower in this game costs more than Peashooter.
 * This is only one of 2 plants in the entire game that can generate sun, other being Twin Sunflower.
 * You can unlock this on the first level, instead of regular PvZ, where it's unlocked on the next level.
 * This plant is in the real game (PvZ).