Never gone with streetwalkers, so I obviously can't comment on prices and reliability.
But there was a sizable contingent of SWs on evenings in and near Oranienburg Strasse in Berlin, and they address you straight away, when they're not seizing you by the arm to begin haggling

Hard to miss them, considering how they're clothed.
Calle de Montera in Madrid is also notorious for having SWs pretty much at every time of the day; I saw many even at noon when passersby and tourists are aplenty.
As Marmalade said, Geneva has a neighbourhood near the station (Paquis area) which is the main SW area - and some salons / massage parlours as well. As said, seems active day and night. Though there's a slow creeping gentrification of the place and I wouldn't be surprised if all that changes considerably in the next 20 years.
Lausanne has a quite limited and very localized scene, officially sanctioned - area has been massively reduced a couple of years ago. Not sure how much SW activity you would find during day time.
Since we're talking Switzerland, if you have a car, Zurich also has a drive-in system with sex boxes, which replaced part of the streetwalking activities.