jarred or ready made sauces are usually high in syns as they do not qualify for any free food allowance. So the syns will always be 1 syn for every 20 calories.
If you have some passata, you can use that as a base for your sauce. You will find heaps of recipes for a bolognese type dish in the recipe section if you have a look. That way you will then save heaps of your syns to use elsewhere in your day.