Street prostitutes generally have very low prices, risk is high for both them and the customers, so you would think it would be more, but alot of them are addicts, so they don't care, they have got it all down to just living from fix to fix. The cops let it go on to a certain extent, for obvious reasons.
Here is the really disgusting thing - the average customer that pays these women $5 could be your husband or your boyfriend. I used to have to drive down one of our major "strips" outside of Philadelphia, and anyone who uses that road knows to stay out of the far right lane cause you always get stuck behind some nice car from the suburbs going real slow looking for the girls - and when you can finally pass the jerk, you see that he looks just like any decent guy driving the family car, complete with baby seat in the back. It is sort of revolting.
The real answer to this issue: want to get rid of the hookers? Leave them alone and focus on arresting the johns. They have ALOT MORE TO LOSE!