A simple way to know costs. Starting at 5k at the first level and increasing by 5k each time. If you want a quick answer to total costs to say get level 10, 20 or 100.
The formula is (2500*(level-1)+5000)*level
For easy and quick results, you can use this calc. This applies to all Ai army upgrades and castle hp. These max out at level 100 which is 25,250,000 gold for each. For all this is 404,000,000 gold to fully upgrade everything in ai and castle hp. There is also slot costs but most guilds will have this finished before starting other upgrades. In total for +10 slots is 110k.
For what the levels give this is what they start with and max at. This is for each class.
|Upgrade||Bonus per level||Max Bonus|
The Base stats on Ai army isn't known but it's based off of a typical level 20. Attack and running speed isn't fully known but dagger rogues are alot faster than archer rogue and other classes.
It's basically mages do the most damage, warriors have the most hp, archer rogues have the fastest Atk speed and dagger rogues fastest running speed.
The cooldowns for spawn isn't fully know but 5 seconds is a good estimate. So maxed it would be 1 second.