It's really not the jars that are the issue, they are reusable until (if) they break. It's the lids/seals, of which the conventional Ball jars must be replaced each time. There are Weck jars and Tattler lids that deal with these issues. I would post an answer but I don't know how available either one is in New Zealand.

Consider posting this on cooking stack exchange. There are a bunch of posts over there about sealing options during canning. I would not recommend using any kind of used lid except for those meant specifically to be reused, such as tattler lids or wreck jars. It's not worth the risk of contamination.

@user1205935, right now not a whole lot but I plan to do a decent amount of container gardening on my balcony once it gets warmer.

@Flimzy, then we will have to agree to disagree. :)

@Flimzy, many times you'll find that by reducing packaging you're going to be using products that also reduce toxic chemicals. See my answer. Many of these items can be purchased in bulk and are from natural sources. It wouldn't make much sense for me to split this into 2 questions and 2 answers.

@Flimzy, it's one question, because I said and.