In my experience it is not possible to get a room cheaper via a broker, than going directly via the hotel website/reservations itself. This seems to be a general rule across much of Asia... quite contrary to the situation in the US/Europe of course.
My starting point is to review options by using www.tripadvisor.com, then use the hotel agents on that webiste to automatically retrieve best quotes. Then go to the hotel sites themselves and cross-check (again this will almost always be online and instant). Remember with brokers websites to check whether taxes and charges etc ('+++') are included. In Singapore they amount to 16% on top of the flat room rate. Also check the refund/cancellation policy. Booking direct always seems more flexible, and note some brokers require you to pay in full on making your booking.
You might find it worthwhile looking at the Rendezvous, Park Royal and somewhat cheaper the Bencoolen Hotel. The former two are S$140+++ or so, well located and well rated. The latter has a poor website that makes it hard to judge accurately, but it is just behind the Rendezvous and it has been recommended to me...