I originally found my ketchup recipe here. I've tweaked it a few times to steam line the process. I've got the taste to where my family loves it.
So, first, simmer until soft:
1 medium onion, chopped - $0.13
2 tablespoons olive oil - $0.18
When that is soft, blend it in the blender with 1/2 cup apple cider vinegar ($0.24) until smooth.
Simmer that with
1 can, 29 oz tomato puree (GV brand) - $1.08
1 can, 12 oz tomato paste (GV brand) - $0.75
1 teaspoon stevia (or 2/3 cup brown sugar) - $0.16
1/2 teaspoon salt - $0.01
I use canned tomatoes with one ingredient: tomato pulp. You can cook down fresh tomatoes to make tomato pulp, but it will take a while. Canned is way cheaper than store bought fresh tomatoes, and they are already closer to the consistency I want.
It needs to be simmered until it reaches the right thickness. I find a half hour on medium does it. It needs to be stirred, especially as it gets thicker, so that it doesn't stick to the pan. It should be refrigerated for a few hours before eating.
This doesn't taste exactly like store bought ketchup, so if you try it, you may need to tweak it to your tastes, adding either more sweetener or changing the amount of apple cider vinegar.
We didn't switch for cost, although the price is good for the amount this makes. We switched because we don't like the ingredients in store bought ketchup. My son loves this ketchup and eats it plain. I don't have a problem with him gobbling it down, as there is nothing in it that is bad for him. In fact, it's really quite healthy. (Click the picture to see color.)
I get between three and four cups from this recipe. That will vary depending on how thick you want yours. I put it in a jar and keep it in the fridge. I've never had a jar go bad, and it takes us a few months to go through it.