By adapting the receipe in the Ball canning book I found a really delicious Ketchup

Ketchup
1 lg. can tomato sauce
2 Tbsp. dried minced onion or 1 tsp. onion powder
1/8 tsp. ground allspice
1tsp. mustard seed (place in spice bag or tea infuser)
1 4" stick cinnamon
1 Tbsp. celery salt
1 Tbsp. paprika
1 cup Splenda (or Splenda blended with another sweetner to further lower carbs)
1 1/2 cups vinegar
Cook sauce and spice 25 minutes. Add vinegar and simmer until thickened. Stir often to prevent sticking.

Yield about 1 quart
Carbs: 1 g to 1 Tbsp.

Now to further the fun.
Take 1/3 cup of this Ketchup and add it to 1 cup Mayo, 2 hard boiled eggs, 2 Tbsp. pickle relish, 1 1/2 Tbsp. onion, 1 tsp. paprika, and 1/2 tsp. salt. Place all ingredients in blender or processor and blend until smooth. This makes a full pint of Thousand Island Dressing with only .7 carbs to a Tbsp. or 2.9 to a 1/4 cup.