I've heard nothing positive about the newer lower end mercs. Poor build quality, exorbitant (more than normal) servicing costs and general reliability issues. No first hand experience mind you, but I wouldn't touch one (even if i could afford one haha). Maybe look at a Hyundai or Subaru in that ~50k price range. The new 3.6 Legacy is very very nice.
Unsure if things a different in NZ or not.