I bought three shirts and one suit at Mode et Creation Pte. Ltd a little over one year ago. The total bill was S$885. The shirts were about S$85 each and the suit was about S$600. I am happy with what I bought and feel it was worth it.
To answer your question about what is reasonable, I don't know. I do know there were stores selling suits for a lot less, and some for a lot more. Took a city tour our first day in town, and during a stop in china town, went to look at a tailor shop. They started quoting S$1500 for a suit, and by the time I walked (ran) out, they were down to S$700 for the same suit.
Hopefully more will post on their experiences.