You may need to check your code. At level 12, I somehow started losing money (-$585 cash at end). I had to go to survival mode (which sped up my cash gain significantly).
5/5, but don't like how last level is based on how often you get meteor. Everytime I got 30-35 kills, they were already at top rung. Only won because I got 2 meteors to bring them back down..
My strategy was go all melee for the first 20 levels. For boss rush, just use full mage gear. Cast Lightning endlessly and heal when you're below 25 HP. Keep melee'ing when you're low on mana and you can't lose.