How much a pet costs is dependant on its level. Consider the Kau is only level one it shouldn't cost anymore than about 80-100 nps. To be on the safe side, I'd recommed having a least 1,000 nps there though as you can never be too careful
Good luck!
To check exactly how much it will cost place all your neopoints in the Bank and then go to this link:
http://www.neopets.com/process_adopt.ph ... ETNAMEHERE
You should get a message that says something like "You need x amount of nps to adopt this pet". You can do it even when the pet is not in the Pound so you know how much you'll need once it goes in.