Anything that grows back is a great money maker.
Back when I was doing market gardening my best seller was salad mix. It was basically red and green lettuce, spinach, chard, and kale, and stuff like orach, corn salad, or anything mild I had on hand. Sold it for $5 per gallon bag, you could probably sell it for $6-7 now easy. I could pick 10+ gallons per hour and if the weather didn’t get too hot I could pick on it for 3 weeks as it grew back.
Herbs are another one. I could pick $50 worth of basil in no time. Other herbs did good too. Ethnic herbs for Mexican or Asian markets were reliable.
Another one is fall stuff like gourds, ornamental corn, etc, or things used in dried arrangements or homemade potpurri mixes. Or anything that was earlier than anyone else had, like tomatoes or peppers or green beans, or grown in a hothouse. Hot peppers sometimes draw a faithful niche crowd, especially the Mexicans and Asians.