I have made stuffed shells before, and the filling is the same spinach-tofu blend I use for the lasagna, but I have never made a creamy tomato sauce.
The whole pan disappeared in about 15 minutes, not good for the digestion, I'm afraid. The sauce is my regular tomato sauce, but at the end I added a cup of cashew cream (strained) and heated it until it thickened.
Stuffing the shells is the most time-consuming part, so just make sure the under-cooked shell is open all the way (not curled under), before scooping the filling into it using a teaspoon.
You can blend your tomato sauce before pouring it on the shells in case you have a daughter who picks out any vegetable pieces large enough to grasp.
garlic, onion, spices: $1
Total to feed a family of 5: