Actually, photographic equipments in Taiwan can be priced more reasonably than those you can find in SG.
First rule of thumb,
AVOID buying from Xi Men Ding, this is one place you will not want to go for equipment shopping, especially if you are a tourist.
In Taipei city, the place to go for such equipments are the shops along Bo Ai Road (next to the General Post Office and a short walk from the Taipei Train Station). It is lined with shops selling all sorts of photographic related equipment. These place stock a wider ranges of products than what we can find in SG. Things like Tamrac bags, Velbon tripods, hard-to-come-by professional films/slides, MF stuffs etc can be found there if you take your time to look around.
Here's a map that I done up, hope it is clear enough for you to get a rough idea :
I normally drive around the city but from what I see, you should be able to reach this place by taking the MRT service from Xi Men Ding station to the Taipei Train Station stop and take a stroll. Do ask around for the proper direction when you are near.
Price wise, and to quote a couple of examples, a Sigma 15-30 can be had for about S$820 (or about NT 15,500 with a little bargaining), complete with international warranty card. Velbon tripods, especially carbon fiber ones, are generally cheaper there too. The 6x0 CF models selling there are approximately S$70 cheaper as compared to SG prices (by what Alley photo used to charge).
The favourable exchange rates in recent months is a boon to such purchases (ie. S$1 to approx NT$19.3) so you may wanna be prepared when you take the plunge cuz they do charge a sizeable "service charge" (about 3-6% depending on shop) if you decide to pay by credit card.
Shops like Jiu Hua (Chilian Co. Ltd), Yong Sheng, and the ones nearer the former are my regular ones, they are quite honest with their trade and have good service attitude. One word of caution though, be mindful of what you are asking for and be prepared of what is a fair price to pay. Try to speak Chinese with them if you are fluent with it, normally, this will help in getting you a better bargain, no kidding
Best of all in your trip and your shopping!