I've made my own for ages now, due to the same reason, and it's cheaper too.
Need
onion, finely chopped
garlic clove, finely chopped
carrot, finely chopped
mushrooms, finely sliced
half stick celery, finely chopped
basil and oregano, finely chopped
olive oil
2 tins chopped tomatoes
sugar
salt and pepper
tomato puree
worcestershire sauce
Add dash of olive oil to pan and gently fry onion, garlic, carrot, celery and mushrooms, 2-3 mins. Add the herbs stirring well. Add the tins of tomatoes and a tblsp of sugar (this takes away the bitterness of the tomatoes) , tomato puree I use 2 tblsps , salt and pepper and dash of worcester sauce.
Simmer for 40 mins until thickened .
If making bolognaise I add the mince, and brown after the veg , if I have any I add a finely shopped rasher of smoked bacon too. Also a dash of red wine into the tomatoes if I have any left.
I don't cover it and let it simmer away, so it thickens , just stirring occasionally.