There are four options to buy sex in Prague; night clubs, Privats(private apartments), escort agencies, and street girls.
After economic crisis, there are more street girls on the downtown streets. They were usually from Northern Africa or Gypsies before, but now you can find many Czech girls on the street. Those are worked at small nightclubs or privats before. I will not recommend street girls because most of them are druggy. Thus, safety will not be guaranteed.
There are a lot of escort agencies in Prague. Some of them are very expensive and some of them are not. Some of them are honest management but most of them are not. I will write guidelines to use escorts well later, but not recommend escort agencies.
I will recommend privats(day time) and nightclubs(night time).
There are hundreds of private apartments in Prague, price ranges are from 500kc/hour to 2000kc, or even more. Many new privats are getting nicer and more expensive. After economic crisis, more privats were opened even though most of small clubs suffered from recession. I can say you could find some nice young girls with good service at privats. But most of privats opens until 10pm, so you