You have to register on TaoBao, then you can click on the buyer's name at the top and instant message that person. You have to download the Ali wang wang IM program, too. Some listings, like the one Human pasted, have buy it now and add to my cart buttons, but you'll have to contact the seller no matter what if you don't have a Chinese credit card; you'll have to arrange payment and shipping.
The seller in the listing you're looking at hasn't sold any of these in the last 30 days, but buyer feedback is good. That's a pretty high price, though. If you contact them, ask them if they speak English, too. Just paste this: 你会英文吗?