I recently did a float rating in Canada, just north of Toronto and it cost me $1700CDN for 7 hours which is about $2400 NZ. If you have a NZ licence than you must apply for a foreign validation in order to get a float endorsement in Canada. You should check to see if the Canada endorsement will carry over to another licence.
As for the Beaver - you won't find anyone offering initial float endorsement on that a/c in Canda unless you go to Georgian Airways in Ontario but you must enroll in the 50hr bush flying program and you'd only get 1 or 2 hours on the beaver.
As for work, can't really help you out much with that - are you looking at work in Canada? If I can remember, I don't remember much float flying in NZ, there was a guy doing stuff somewhere on the North Island on a 182 but that's all I knew about. If you are looking at Canada - good luck! You;ll need a minimum of the 50hr and will probably only get a job as a dockhand for a year or so... lots of competition.
Good luck