Following some comments...
The Indian ladyboys would be around houses 31 and I think house 51. I understand they come from Malaysia. A number have got good figures. Not tried yet.
Some of the ladyboys can give as well as take. However because of their hormone intake (to enhance their feminine qualities), this is sometimes a problem. So, you've got to actually ask. They may ask for an extra 10 Sing bucks or so for them to pound you.
Normal service is about 20 minutes, hence the low thirty dollar price. However, you could ask for extra time in exchange for extra money. Some would do half an hour extra service for forty dollars, for example.
One idea would be to take one and build from there. Once you take one, the others will see you as a serious customer and pay more attention on your subsequent visit.