Orchard Road is Singapore's busiest shopping street. One end of Orchard Road, in the vicinity of the Hilton Hotel, is where you would find a decent selection of upper end ladyboys. They operate mainly around an oldish building called Orchard Towers in 2 bars - Crazy Horse on the fourth level and Club Romeo on the third level.
In the former you could see about a dozen and in the latter about eighteen. These Thai ladyboys start coming in from about 9pm and the idea is, you buy them a drink at either bar and negotiate your price over a drink or two.
Incidentally these cost S$18 in Crazy Horse and now $30 in Club Romeo.
They would charge S$200 on average depending on your needs, their mood or what they think they're worth. (Room and taxi not included, usually S$30 for 2 hours plus S$10 for taxi if required)
Your other option would be to come around midnight where free lance ladyboys from Singapore, the Philippines and sometimes even Cambodia or some claim Vietnam would appear.
They would strut their stuff on the ground level of Orchard Towers right up to outside a department store called Isetan. Here asking prices are usually more flexible although S$200 seems to be the favourite asking price as well as the room and taxi.
Prices cannot be compared to Bangkok, for example, due to the relatively small number managing to get through Singapore immigration.
Generally it's a wise idea to include your preferences whilst negotiating price.