Una Queen
Squire
I told him itd cost something like 30k or something at start of the event. it was just a number I thought itd cost as he is unable to purchase things in this game because of the country hes in so he cant buy the event pass nor diamonds so he has to use diamonds he earns from ge, gbg and diamond farms. so he decided against getting a second one.It's difficult to give a accurate number on that due to the nature of the mini-game. It would depend on what strategy your friend is actually using.
Are they intending to clear the board every time and do a spending spree in a single sitting?
Or are they using the reset option?
If they're using the reset option how many times are they going to reset? The reset cost if you don't clear the board goes up each time.
My suggestion would be to gather a decent amount of currency. Write down the amount of currency you have. Do some boards. Do some chests with the keys you earned. Now write down your remaining currency total, work out how much currency you used total. Look at your Grand Prize progress, that's how much that amount of currency bought you.
Now look at the currency shop and look at how many diamonds it would have cost to make that amount of progress.
From that you should have enough info to work out how many diamonds it takes roughly per 1 Upgrade of the Tower.