There isn't any fixed rate places in Prague. There was a private once where you go in for a hour and fuck three girls. It was not a success. The place has now gone.
Haven't come across any club like Insomnia.
Showpark Market is very good (imho)at weekends and you can use the entrance ticket for 24 hours. You can also use the ticket at Showpark Da Vinci, which is close to IP Pavlova metro station. Google there web sites.
Also look at
External Link/Members Only and escort cz.
Hope you enjoy your visit to Prague it is a wonderful place to visit.
PS. Unless you just want to just have drink and eyeball the talent on show ,steer clear of the big clubs just off Wenceslas Square Like Darling,Atlas and HotPepper's and the like or you will get taken to the cleaners.