Penny Pincher

This Achievement can be done at any level, including Adventure mode, if enough coins are dropped. The best levels to do so are Survival: Endless because large waves of zombies arrive, however, you can't let any disappear, or this achievement will not count. Playing the Last Stand mini-game and using Marigolds or a Gold Magnet would be a good example. Another would be playing Whack a Zombie because the zombies drop coins very often here.