This is a very big question, difficult to answer.
Go into a good bookshop, buy a copy of the Lonely Planet Guide to New Zealand. That will give you a lot of information about the country, distances, accommodation, costs etc.
How do you intend to travel? Car, Campervan, public transport? Where would you stay? Hotels/ motels, backpacker lodges, camping grounds etc?
Bear in mind that the NZ Dollar fluctuates in value against other currencies on a daily basis. Check with your bank on the exchange rate with your currency.
Fourteen days will enable you to barely scratch the surface! Perhaps the easiest way to cover the country in that time may be to take a coach tour arranged by a travel agent. Accommodation is prearranged, all meals are provided, the tour guide arranges everything, all you do is go along for the ride, all the 'worries' are attended to for you.
Waikato Lodge of Research 445