Cheapie starters - a slice of melon with a sliver of ham or goats cheese. Half an egg devilled (yolk removed, mashed with paprika and mayo, piped back in) on a bed of salad leaves, a cup of cold summer soup, Welsh rarebit, a chunk of cheapish pâté with thin toast.
Cheapie mains.
Risotto.
Casserole - frozen chicken thighs or pork loin is pretty cheap at the moment - with baked potatoes. Don't bother with baking potatoes, just grab the larger ones from the cheapest bucket at the supermarket. Or roast new potatoes.
Lasagne - stretch the mince with lentils, and bung a bottle of wine in the sauce if they have provided generously!
Pizza also not expensive if you make the dough yourself. Not hard but a little time consuming (or 15 minutes in bread maker plus time to prove). Once you've got dough, easy to make lots of different pizzas. Traditional tomato sauce, then mozzarella and more ham, pineapple, that sort of thing. Bottle of BBQ sauce, cheese, then chicken, bacon, sweetcorn, onions. Just pesto on the bottom, then garlicky cheese, olives, courgette ribbons. Tomato, with tuna, sweetcorn and olives. Whatever floats your boat. But with giant salad and garlic bread it's tasty and not pricey. Oh, goats cheese and red onions a nice gourmet-y type topping too. Pesto and walnuts.
Great big bowls of leafy green salads, lettuce not at all pricey right now and goes miles!
When we are doing bulk catering, we cook up a ham, cheaper than buying small bits. It gets sliced cold for lunches and thicker slices do a nice gammon style meal with pineapple rings and fried eggs.
We do a great bucket of potatoes which get served cold as potato salad, hot with evening meal, and sliced and fried with breakfast too.
Other breakfasts - porridge or buckets of Greek yoghurt (cheap in lidl, decant into fancy bowl if they are food snobs), with fresh fruit, dried fruit compotes, muesli, maple syrup.
Pancakes not expensive, either fluffy USA ones for breakfast or traditional crepes as a pudding.
Other puddings - big vat of crumble or sponge, meringue if you have a friend with chickens, bread and butter pudding, rice pudding all pretty cheap to make in bulk.