If you want cheap t-shirts, polo shirts, any shirts, go FOS at Meridien Hotel Orchard. It cost around $12.90 to $15.90. You can try Ebay too. Also see This Fashion. If you want branded ones, go to Takashimaya Polo Ralph Lauren and any sporting store.
Anywhere in China can run these off for pennies ... however you have to watch out for scammers (they supply really good quality samples & then either ship rubbish by the container load or don't bother to ship anything at all). (Other possible sources...
No. The women's shirts are too flowery and look like they were designed using clip art. The men's shirts are not anything different. They look like cheap knock-offs of Affliction shirts.