OK, running a bit of an experiment here. Partly because I am a fat lard and partly to see if it really is cheaper in the mid-run to eat healthy.
We know it's cheaper in the short run to eat crap...the dollar menu is ...well.. a dollar. So if you can get one or 2 or 3 items and pack in 1000 calories you're going to feel more full and make it through the next several hours. However, by the end of day 2 of eating the dollar menu, you're going to feel like crap and realize that you'll ultimately spend more. BUT if you live somewhere without easy access to fruit and veg, without space and ability to store them (e.g. roach infested inner city apartment complexes are rarely near a good produce market and you can't store things without them getting ruined), then the savings of shopping for fresh fruit and veg may indeed NOT be there.
In the long run, when you consider health care costs it's always better to eat as healthily as possible.
But what about the mid-range. Weeks or months?
I'm trying to eat a minimum of 4 servings of veg and 3 servings of fruit per day. In the short run, I'm too stuffed with salad to eat much more at lunch so that is good. But, organic salad is not available in my home town and I'm only in the big city once every two weeks or so. That means that I run out of organic salad in one week and have another week staring me in the eyes. Organic salad is also expensive. Hence more root veggies. They are healthy, store well and taste good and are fairly cheap. I've also been buying...industrial fruit and veg at the local store. I could probably get over the pesticides but I really resent all the plastic packaging.
After 1 week in, I've spent more on groceries than before. But that is partly due to coming to the end of most of my winter stock of veggies other than the squash. Still have quite a bit of lovely squash. And partly due to not having enough stored whole or frozen fruit and being largely out of dried fruit. It was a bad year for fruit last year and it's showing. I have some slightly soft apples left but those need to be in a salad or cooked or they are pretty unappetizing even though perfectly consumable. A few dried pears left. And quite a bit of plum sauce...must find more uses for plum sauce.
I think when more fruit and veg is in season and if I can get the sprouter going again full steam, it will be thriftier in the mid range to eat lots of fresh fruit and veg.