Scrypt's maximum strength to increase entropy of lame passwords The developers claim that a 6 letter long password hashed with 3.8 second's of scrypt would cost $900 to brute-force. 


If we use more cycles, how quickly will the brute force cost increase? 
What are the minimum system requirements to compute such a huge KDF on a desktop or mobile?
Is there any formula to estimate its entropy based on CPU cycle time?
Does Scrypt survive from Grover's algorithm?


Please consider that bad passwords can be very long.
You have to test it on the hardware you'll be using. I tried CryptSharp's implementation with a cost of 262144 and it took about 7 seconds.
The reason it costs more is cause of the memory it uses, and my process that was running the Scrypt was eating up 340ish MB.

How much of that was from the KDF? Don't know.

How would my box handle 100 people authenticating at the same time? Very good question.

This is something you need to performance tune to specific hardware.