which brand are you looking for? go to the sub-forums of the respective brands and the price lists are at the stickies. if im not wrong the accessories list would also include a list of reputable shops in SG. do note though that there has been a recent price increase, so prices may be a little off. you could call the shops for current quotes.
I'll help you get started. If you notice, each individual section has their stickies. For example, the sub-forums for camera brands (Canon, Nikon, etc). Don't overlook them: They contain all the information you need. Like this thread: It's the compiled price list of all the Canon lenses available (however, this list is maintained by our members once in a while and thus you should still contact the shops to know the correct prices since it may be outdated).
Also, here is a compiled list of the shops in Singapore. Use it as a reference, if you want to know the shop's reputations, do check out the other threads/stickies in the forums.
Remember, there is a search function on the top forum menu (third to last on the right). It's your best friend here.
But, just to help you cheat a bit: I bought my Canon 50mm f1.8 from MS Color for $110. Next time, do remember that the answers are already here, you just need to know where to find them. (Oh and just because you're looking to buy something doesn't mean the information is always in the Marketplace. Expand your search!)