To order from taobao, you need to go through an agent, since the only way you can order is with a Chinese bank account. There are many agents out there, I personally use taobaotrends, but I've heard good things about taobaonow and taobaospree. These agents will place an order from the listing in your name, the standard procedure is to copy and paste the url of the taobao listing into the shopping basket on the taobao agent's site after joining and placing an order. Keep in mind that taobao agents charge fees of their own on top of shipping fees, they usually add up to around 10 percent of the total cost.
The type of listing and currency conversion also has to be taken into account. The listing you linked lists multiple items, kind of like in ebay where they have listings with drop down lists and you get to choose which item you want, so this listing isn't selling all the zelfs for the listed price, they are priced individually at about 11.38 USD. Not all of them appear to be in stock either, you can see which ones are in stock by clicking the little images below the price.
To order from this kind of listing you have to be very specific with the agent about which kind of zelf you want. This can be tricky, try and use simple words to get around the language barrier. For instance, if you were ordering Buttershy, specify that you want 'pink toy, yellow hair, butterfly wings'. Most taobao agents will have a text box where you can do this, and some agents also will send you a picture of your order before shipping it so you can verify that they ordered the right item.
Lastly, keep in mind the time it takes for the item to get to the agent, then to North America. Since the party is in 3 weeks, it may not arrive in time using regular airmail which in my experience has taken up to a month in some cases, so you might have to add a little extra for faster shipping on top of the agent fees or look for them elsewhere.
Here's some more info on buying from taobao. Hope you found this helpful.