Everything and I mean everything is getting more expensive. It's especially egregious with basic needs like food, clothes and shelter.
That said, the cheapest way to get fruit is going to be local and in season. Look up your local farms and go to them. Even then, you gotta keep a bit of an eye out, as I've noticed some by me have been charging ridiculous prices for pick-your-own, pitching it as an experience for the kids and asking a premium for that.
When you get local fruit, the best way to keep it year round is to either freeze it or preserve it in jams, pickles or what have you.
It's gonna be hard to get fresh fruit at a decent quality and price in the cold months. Fruit doesn't grow then. Simple as. That said, I often see deals on bags of frozen fruit that makes it somewhat more affordable vs fresh during winter. These tend to be lower quality, so I end up macerating them with sugar and making baked goods with them, or mixing them with yogurt.
Oh and citrus. Citrus seem to travel well enough that you can get decent citrus year round.