Also, healthy food is cheap, but people buy junk because it is superficially more fun. Compare what you get from $10 of Lucky Charms vs $10 of veggies, beans and cheese, and, if you must, simple bread and low quality cuts of meat.
$10 in dried beans is lunch for a month, but it's damn inconvenient, and yes, difficult to make taste good.
These are both extremes but yes, I am very confident that healthy food is more expensive than less healthy food. Yes, a cucumber is "cheap". But 8 cucumbers (.50/each) isn't going to get you nearly as far as a 6pack of GV mac and cheese ($3.98). Not even the same ballpark. 5 servings of GV thin-sliced honey ham costs $2.50, a loaf of the cheapest white bread is $1.50, 8 servings of GV block cheese goes for roughly $2.22, so now I have let's say 10 shitty sandwiches for roughly $8, when I could have had easily 12 meals of mac & cheese for half that and with less prep time.
Where cheap and healthy come closer together, I see the staples of my (well, my friends', but that's another story) childhoods; lots of potatoes, scrambled eggs, beans.