Cheapest Team To Level Up?

I've decided to do research to find which team is cheaper to level up and which more expensive. After doing some research the cheapest team to level up is fire team. It's obvious that most of the people don't use fire team. People only use fire to do daily quest. Also fire team has no any significant advantage over other team. Maybe that's why fire team is the less popular one. Second cheapest to level up team is earth team. The most expensive teams to level up are dragon and death team. In my opinion death team is the most loved one. To buy death rare death summoner you need to spend approximately 0.70-0.80 usd which is 2 times more expensive than fire rare summoner.