Plenty of import agents around, I use Mainfreight International for my clearances. As FT said, make sure you know what it is packaged in, or risk big quarantine charges. Best to find an agent, explain what you want and ask them about steps to take to make it all happen. You will have Duties charges (don't know the rate, maybe 10%), GST (10%), sometimes airline handling charges, storage charges if it is at the airlines more than a day, handling charges if it is coming in via sea freight, and agent charges.. You can save a bit of money if you get the agent to do all the clearance and turn up with your documents to collect yourself, but this is often more hassle than it is worth if coming by sea.
Get your seller to email you scanned copies of all documents - airway bill, commercial invoice etc so that you can send to your agent to get the clearance happening before it arrives.