So how much Hive did it cost to print 20% over the last year?

The effect on Hive only materializes when people start to unstake HBD and convert it to Hive to pay out their interest in USD. Then the money is drawn from Hive as a collateral at the current Hive/HBD price.

20% being unsustainable

Do you currently see a year on year growth of 20% on Hive? In the long run it is unsustainable because every APR greater than 0 leads to exponential growth. It is just a matter of time.