I wouldn't bother importing memory sticks.
The pricing here is pretty similar to China.
You can check retail pricing in China on
http://newegg.com.cn or
http://jd.com
In China usb sticks are called upan - u盘
If you read Chinese, you can check taobao (
http://www.taobao.com ), but I'd avoid the lower end priced stuff, as there are a lot of fakes. If its too good to be true, its too good to be true...
You can ship airfreight 1 week from China for 150RMB/kg, usb disks weigh virtually nothing, so you could ship 30-40 pieces.
Customs here can be rather random on charges though. You may get hit for clearance charges, you may not.
In order to check the tax + duties for a product, you'll need to check the HS Code (Harmonised Standard Code) for the product.
USB Sticks are computer accessories, and zero duty, so you just pay tax on the shipment + clearance charge.
If its for personal use, you can bring in a small amount duty free - can't remember offhand, but its a few hundred rand I think.
You'll also need an import licence and vat number if you're doing it properly.