Welcome to the rollercoaster
It's a bit of a stressful journey but well worth it!
Yes, you will need to have a medical as part of the visa process - once you have got your main visa application (not for the basic Expression of Interest part if you are going for the Residence Visa)
When I did it in mid 2009, it cost me somewhere between £250 and £300 for both me and my husband (I don't have the exact figures). You need both a medical assessment, including blood tests and a chest x-ray, and it needs to be from an approved doctor (there's a list on the immigration website - http://www.immigration.govt.nz/branch/ApiaBranchHome/paneldoctors.htm
). Because it's a private appointment (even if the doctor belongs to an NHS practice), you don't need to go to your nearest one, so it is worth shopping around, as there can be a difference in price!