Although Prostitution is legal in Italy soliciting isn't, and because of the Vaticans influence it is very hard for Prostitutes.
They can be found at the following places:-

around EUR quarters from about 9.30 pm to 2.30 am. Usually business is carried out in the car, but some also provides a room. The girls are from eastern europe and Africa, with some Italians as well.
Prices range from $20 to $30 in your car, and from
$75 to $100 in her room. The girls provide condoms.
Mattatoio zone at the cross "via Prenestina via Palmiro Togliatti". It's a peripherical zone.
Acqua Acetosa zone :take "via Olimpica "
direction "Foro Italico" exit "Parioli" along with "via Acqua Acetosa"