I grow cayenne peppers to save money. One plant yields so many peppers that it's legitimately profitable.

I do save money growing mint over buying it at the store, because mint is eternal. I've been making juleps and jelly out of the same mint plant for about 6 years now. But mostly I keep mint around because I like it.

Tomatoes? It's not really about the money, it's that grocery store tomatoes are designed for durability rather than flavor.