There's different kinds of "bang" for the buck. From a pure compared-to-supermarket-prices perspective: shallots. I've seen shallots go for a buck each around here. I bought a bag of sets for 16 bucks years ago and save some back for replanting every year, so my cost per shallot goes down every year even as my crop size grew. As the numbers are currently working, each shallot I grow this year will cost less than two cents. Plus they are terrific to have in the kitchen (especially when they are cheap) and offer long storage with no special effort. From a nutrition-per-square-foot perspective: potatoes. A ton of food from small spaces. Also superb in the kitchen, especially new potatoes, and interesting variety available. And also offer long storage without canning or freezing. From a gee-whiz-in-the-garden perspective: Swiss chard. Grows from spring to fall, is hardy and likes cool weather yet also yields in summer heat, yields all season from a single planting, is easily grown and rarely bothered by pests (in my garden anyway) AND is best thought of as two vegetables culinarily (leaves and stalks)...whew, that's an impressive list of credentials for a leafy green! Collards come close, but I find chard easier to care for and more interesting in the kitchen. But my overall champion has to be: tomatoes. Easy to grow. Prolific plants. Great compared-to-market value. Almost mythical quality when garden ripened. Tremendous variety to choose from. And, for me, without a doubt the most versatile vegetable in the kitchen. They can find a place in breakfast, lunch, or dinner. They can be raw or cooked a million ways. Consider the number of cuisines they are at home in, and the number of roles they play in those cuisines, and the number of ingredients you can marry them to - it's amazing. So for me they are an unbeatable combo of money bang, garden bang, and culinary bang.

how much are you watering. is the ground still wet? what kind of fert are you using. looks like a nutrient and low light problem. nutrient problems can be caused by not enough or to wet soil. listen to jean001a.

Have you been fertilizing? They look relatively healthy, though they could benefit from some fish emulsion or miracle gro.

Photo not clear enough to tell for sure, but it's a good idea to spray fungicide on cucurbits to prevent PM before it takes hold.