Triple Town Economics (How to Never Run Out of Turns)

When I first started playing Triple Town I was annoyed that I kept running out of turns. It felt like the kind of dirty trick a Facebook game would play. Actually, I just wasn't good at the game. It is possible to earn enough coins from each game to pay for your next game. It also makes the game more fun: instead of bears being troublesome creatures messing up your high score, they are profitable resources to be exploited.

Ironically, now that I don't need unlimited turns I bought them anyway because I want the other game modes.

The economics

1. Turns cost between 0 and 4.75 coins/turn, depending on how much play per day (because you get 150 free turns per day). Example: 150 free turns plus buying turns twice: 550 turns for 1900 coins, or 3.45 coins/turn.
2. You get paid 1 coin per turn (at the end of the game). You also get paid based on your city's rank, but I'm not sure what the formula is so I don't worry about it.
3. Mansions pay 100 coins each (at end of game). Castles pay 200 coins, but require 3 mansions, so it is better to just keep the mansions.
4. Treasure chests pay 500 coins.

For the example 550 turn game, you need to make 1900 coins total. You'll get 550 coins (#2 above). If you can get 3 treasure chests, you made a small profit. Or if you get 2 treasure chests and 4 mansions, you also come out ahead.

Further Nuances

1. It takes 27 bears to get a treasure chest (bears -> churches -> cathedrals -> treasure), so a correctly-placed bear is worth 18.5 coins.
2. A crystal used to combine two cathedrals to get a treasure chest is worth 167 coins (1/3rd of 500)
3. A crystal used to combine two houses to get a mansion is worth 33 coins (1/3rd of 100)
4. Using crystals & robots to make rocks -> big rocks -> treasure chest requires 7 crystals and 1 robot. 71 coins per crystal. You're better off using crystals to combine cathedrals, except...
5. At the start of the game you get lots of crystals and sometimes start with a couple rocks. If you get crystals before you have anything useful to combine, the rock -> treasure route is reasonable. This can be a quick way to pick up 500 coins at the start of a game.
6. All those crystals at the start of the game also mean the early game is more profitable. Once the crystals stop coming and the map is filling up with ninja bears, it is time to scrap the city and start a new one.

(I play the Android version of Triple Town. I don't know if the iOS, web, or kindle versions have different economics, but you could do the same analysis).