buy a 28oz can of crushed tomato (i like hunts brand)
mix it with your standard jar spaghetti sauce in a pot on the stove.
add 1/2 cup - 3/4 cup of water (can be omitted)
add a tablespoon of salt, and a healthy pinch of sugar (sugar can be omitted)
add seasonings like basil, oregano, garlic powder, and crushed red pepper
let simmer on stove for up to hour
you can more than double the sauce you have and in a pretty cheap way! also once it’s cooled you can freeze it.
I never even buy actual sauce anymore. I always use crushed tomatoes. Generic brand is usually around a dollar, Two of those, plus a can or two of diced tomatoes, pretty good base sauce. Then you can just add whatever you like. I usually go with an onion, mushrooms, and either sausage or ground turkey. Its several meals for around $10.
The sugar mentioned above helps to cut back on the acidity of the sauce btw. I usually try and use some if I have sugar at the time.