I've never paid for a basic eye exam in Singapore. Its always been complimentary if you buy the frames and lenses from them. my last two pairs with the scratchproof lenses were both around SGD200, far cheaper than similar choices in Detroit and London, just for a frame of reference.

edit: I went to Spectacle Hut at Plaza Singapura and Koolook at Suntec the last two times, before that usually Nanyang Optical at Parkway Parade.