Hate to be a food purist (again ), but dim sum is a Cantonese thing, and Singaporeans for most part aren't Cantonese -- which is why dim sum isn't nearly as big a thing in Sing as it is in Hong Kong.

That said, I'm partial to Jade at the Fullerton, their weekend dim sum is not particularly authentic but is pretty darn good. $40++/pp last I checked, although this has probably gone up. (For comparison, at dinner time, most single menu items have triple-digit price tags.)