Question about upgrade costs

[rub1x]

Can anyone confirm the costs to upgrade the Sparkling Mine and the Sawmill beyond the 1st upgrade?
Does the cost remain constant, increase?
And does the amount of time decreased remain at 12 minutes per upgrade?

[brandonu]

The cost of items (rarer items) increases with each upgrade, as does the amount of coins needed.

The time decreases by 5% each time, but I believe off the original 4 hour time.

[lotuskat]

Yup, the Level 2 Sparkling Mine costs 5 wisp lanterns, 3 stone blocks, 5 wooden beams, and 30k coins.

[cloudsail]

You need a golden nugget to upgrade mine beyond level 2. Pretty cool, first use for extra golden items that I've seen.