This is an important topic to me and I have been giving your question a lot of thought - bottom line - I couldn't come up with any better
answer than dehydration.
All other methods of safe preservation seem to require resources/inputs such as electricity, additives, prep time and so forth.
I ended up going the dehydration route. Last year I bought a very well reviewed, semi-large capacity dehydrator. The company said that in the most expensive areas of the country that it should cost about 6 cents an hour to operate it. So if I pack it to capacity and run it for 18 hours then I have spent 1.08 US. Since my electricity is a bit cheaper than that and I don't ever run it on the high setting then my cost is even less.
I dehydrated pounds, and pounds, and pounds of produce. The tomatoes were gone within just a couple of months because they were so good. We make all of our own garlic and onion powder now with the dehydrated onions and garlic. I could go on and on.
If you open a jar of food and it feels a bit soft but does not smell or have any signs of mold you can just pop it back in and dehydrate some more.
I am still working full time, learning how to raise meat and egg birds, trying to grow all of our food, work a garden at a museum and sit around and surf the net like I'm doing now ---- Dehydration is GREAT, it takes virtually none of my time.
I know you said you didn't want to use that method but I just had to put my two cents in about it because I had been looking for easy safe ways to preserve food that were not dependant on long term
energy use (freezer) or required a lot of my time and or knowledge to prepare (canning). And I didn't want a bunch of sugar (jelly/preserves).