A level 10 wall cost a total of 3 million. If you want to upgrade your wall from say level 4 to level 10 ,it would cost a total of 5.45 million coins
It costs 4 million gold per level 11 wall
5,000,000 elixir
1500000
2,750,000 elixir, but you get witches.
2,000,000 elixir (2 Million)
Barbarians, Archers, Goblins, and Giants
It is really up to you. If you want your dragons to become more powerful, 20 more damage per second and 200 more hitpoints, then upgrade the dragon. If you want to be able to train P.E.K.K.A's then upgrade Barracks to level 10. But you could actually do both at the same time. While upgrading barracks to level 10 (2 million elixir), upgrade your dragon to level 2 in the laboratory (2 million elixir).
Anything you can chose between giants and archers as they are the most useful troops in clash of clans and are pretty cheap too. So you should upgrade them first.
In clash of clans, the maximum level on balloons is level 8
At level 1 it costs 15000. It increases by 3500 every upgrade.
Level 15 walls do not exist in Clash of Clans, although they might in a future update.
180
The price goes up some per level. The first upgrade is 10,000 dark elixir. By the time you reach level 40, it will be 190,000.
It takes six days to upgrade to Town Hall level 7.