Six Flags Great America in Gurnee Illinois 

The prices are, $80, $100, and $160 per person for the Flash Pass during the weekdays and $90, $110, and $185 during the weekends according to SixFlags.com. Did not purchase the Flash Pass but there might be lines and waiting time at the ticket windows. Guess the question would be do you want to wait in the line to buy the pass there?

as Travel Peter already mentioned, i try to get into the park first thing when it opens and there is always a line of people waiting outside the Flash Pass store at park open since quantities are limited

It was last weekend.

@@TravelPeterK i dunno if you were there on Sunday but man the waits were freaking awful...worse than usual honestly. There was even a 20-30 minute wait for the pirate ship ride of all things

Not very good at talking. :}