Jess, have a look at ero.govt.nz, they have a list of childcare places in your area. Then you can have a look at the reports on the centres to see what they say about them. Once you have got a list from there of one you like. Ring up the places and ask to go and have a look. They usually say not between 11am and 2pm as thats lunch and sleep time so try and make the appointment for just after 2pm so you can se how things are at a rush time. The person that takes you through should give you an info pack on the place and it should include a price list and the min hours they can be booked for. Also you could be eligable for the childcare subsidy so have a look at that as well workingforfamilies.govt.nz.
As for places in Welly, sorry can't help. My sister is a nanny done there so I could see if she has heard of any places for you if you want.