Hi Kate,
It's near impossible to answer your question without knowing more about your tastes, needs, and tolerances. You'll find rents (and food costs, believe it or not), all over the map, depending on where you want to live. How fancy or 'rough' the barrio?, the commute distance/time/hassle to microcentro?, proximity to parks or milongas?, size/view/noise considerations?, duration of your lease (cheaper 2-year leases require a garantia and funiture)?, your budget for rent?, your tastes/needs for restaurants, taxis, etc.etc.
Speaking of budget, it's kind of important to know what you can afford, what kind of a job/salary you expect to find. Use the Search function on this forum to read up on the 'challenges' finding decent-paying jobs, ideally those paying in Dollars or Euros rather than in Pesos. Also read up on threads in this forum and BANewcomers Yahoo Group re: housing & food costs over the last year. It really depends on you--wouldn't be good to have Recoleta tastes with a Flores budget (sorry, Floresinos).
You say you've been here, why not come for an extended visit, dip the toes in the water a little deeper, plan to explore some barrios and see for yourself, see if you still love it, not as a visitor but as a resident? Just as you couldn't really "get a feel for the cost of living" in your visits, it's really hard for any of us to get a feel for your desires & tastes. One thing many expats agree on: it's usually easier to 'make money' at home and then bring/spend it here while you get established, find work, learn the tricks, and decide if you can survive and thrive here on your savings & local salary.
Good Luck!
(and remember to convert those kiwi dollars to US $100 bills before coming, to use for exchange!)
- Jim