How to 'stretch' tomato ketchup? Currently, my home ketchup recipe involves using around 2.2 pounds of canned tomatoes to make 3.4oz/100ml of ketchup. 

A full can of tomatoes costs me around USD$4.50 here. This means that 3.4 oz, or 100ml of ketchup costs me approximately USD4.50 to make. This is quite expensive if you compare to a bottle of Heinz ketchup which costs onl USD$2.80 for a whopping 32 oz/1 litre bottle.

How can I 'stretch' my canned tomatoes so that I can make more ketchup out of it? 

I have thought of adding corn syrup. 

This is my full recipe:
2.2 pounds of canned tomatoes
350ml white distilled vinegar
1 tablespoon lemon juice
100ml of water
45g sugar
Salt to taste


Add water and blend the canned tomatoes using a hand blender or food processor.
Run the mixture through a fine mesh sieve twice, until you get all the juice out.
Add the juice and vinegar to a saucepan and simmer the mix until you reach your desired consistency. It normally takes me 2- 4 hours to reduce it fully.
I think your answer is found by responding to the question: "Why do I make my own ketchup?"  Heinz ketchup is delicious.  It is also produced in mass quantities.  You'll never compete on cost because of economies of scale. If you are purchasing ingredients, homemade ketchup is just going to cost more.  This brings me to the question I posed.  If your answers are "it's fun"...."I like the flavor"...."I prefer my ketchup over Heinz"...anything along those lines, you may just have to accept that yours will cost more to produce. Maybe find a way to buy tomatoes in bulk? You might get even closer if you grow your own tomatoes. Even then, the cost would likely be more when you take all of the production variables into account.  Any "stretching" will change your recipe, probably at more cost, possibly at risk to the flavor you have developed.  If you are trying to make ketchup to save money, there are probably more impactful home financial strategies you could employ.