Except for a handful of gourmet varieties, all ketchups start with some form of tomato -- either paste, puree or concentrate, although some gourmet brands use whole tomatoes. For that characteristic sweet-tart balance, everyday ketchups use corn syrup and vinegar. Gourmet brands are more varied, using sugar, honey or maple syrup, and sometimes red wine vinegar or apple cider vinegar. Some specialty blends add heat with horseradish, chile peppers or curry spices. Salt, pepper, onion and garlic are common seasonings, too.
Nutritionally, gourmet and regular ketchups are pretty similar. Most have 15 to 20 calories per tablespoon, and no fat. Carbohydrates and sodium are minimal. The tomato itself provides a little vitamin A. Whole tomato ketchups have the highest amounts of lycopene, a phytochemical thought to help protect against cancer.
Prices, on the other hand, vary widely, depending on the brand, shopping venue and whether the ketchup is organic. Boutique bottlers that sell online tend to be the most expensive, but even a "budget" gourmet ketchup will run two to three times more than popular brands you'll find at the grocery store.