What is the DC and how much does it cost to repair a Sturdy Shield?

It is 4th level (Hardness 8, HP 64, and BT 32), and has taken 30 damage in the last encounter.

How many times do I have to roll what DC, and how much does it cost me?

I have found Repair, but I still don’t know the DC (it is not listed at the item), and it doesn’t even mention the cost.