For non-perishable staples, we do a combination of costco and stocking up as much as possible when a really good sale comes up. I don't keep a formal price book, but I have the Costco prices of pretty much all of our "core" items memorized, so it's easy to then scan the local grocery circulars each week and see if they are offering a Costco-beating price.
We have actually found frozen vegetables to be relatively expensive, so I just keep a few bags around for "emergencies" but mostly skip them otherwise. If you haven't already, I'd advise you to figure out which produce items in your have variable prices (i.e., tend to periodically go on sale, or have a season when they are especially cheap), and which items have relatively invariable prices (never/rarely go on sale, no real discernible seasonality). In our area "invariable" items are mainly onions, garlic, kale, spinach, cabbage, carrots, parsley/cilantro, mushrooms. Variable items are broccoli, bell peppers, zucchini, green beans, brussels sprouts, winter squash, tomatoes, most fruit. For the invariable items, I buy the more expensive stuff (mushrooms!!) sparingly, but use the cheaper stuff (onions, cabbage, carrots) pretty regularly and will often use it to "fill out" a dish that also has expensive vegetables (for example, we love to make a big mess of sauteed peppers and zucchini in the cast iron skillet. Adding an onion lowers the cost of the dish and tastes pretty good too). For the variable items, I keep an eye out for sales or wait until they are in season, then use with abandon.
I don't really figure out exact cost per meal, instead I just try to gravitate towards using more of the cheaper ingredients within a certain nutritional profile/category. E.g. beans are cheaper than eggs/milk are cheaper than chicken is cheaper than beef. So we eat a lot of legumes (black bean soup, mmmm), a fair number of eggs, occasional chicken, and very occasionally beef. I do periodically calculate our average cost per meal per person and try to keep that average pretty close to $1.50, which I know is higher than the $1/person that MMM has sometimes cited, but is still pretty good compared to typical household spending.
In terms of whether or not you are cooking "more calories than you need to" into a meal: Are you/your family overweight or gaining weight? If you're at a good weight for your size and maintaining it, you aren't cooking with too many calories. If you do want to lose weight or think you are experiencing diet-related health problems, you may not need to cut back on oil specifically. Like someone posted upthread, fat is not necessarily bad, so you may just need to trim back on portion sizes.
We also do a lot of freezing, mostly of soups/casseroles/stews. Some favorites:
-Black bean soup
-Tomato soup
-White bean & garlic soup
-Tom Ka (coconut based, so yummy but maybe a little spicy for kids, though you could certainly tone it down)
-any kind of curry (for a kid, maybe something like this "starter curry").
-Butternut squash/pumpkin soup
-tomato-lentil casserole
We'll usually defrost and then serve with a side salad or some kind of easy vegetable dish (steam/saute, etc.). Another vegetable dish that we are LOVING lately is cauliflower "rice" (grated/finely chopped cauliflower, cooked and seasoned). It is pretty easy and I think might be reasonably kid-friendly--it doesn't *really* taste like rice but it doesn't really scream "VEGETABLE" either. For snacks, we do mostly do raw fruit and vegetables and nuts, with hummus or nut butter for dipping. Very fast and easy!