For Custon Shirts, William Cheng & Sons, 38 Hankow Rd, 8/F.
I always visit and was there about a month ago. Excellent selection of material on full bolts (not just swatches, like most storefronts). They will make a shirt however you want it (tight neck, or waist, loose fit etc.) Just be sure that they understand your requirements during the measurement process.
I paid about 250 hkd EACH. I find it impossible to wear out these shirts