Along Kim's ideas of adapting your current recipes...stick veg in everything! It reduces the amount of meat you need, which also reduces cost. Of course, there's still lots of ingredients (vegetables) - but you need to eat lots of veg for a healthy diet anyway, so that's a good thing!
For example, I made chicken tacos last night - bugger the 'kit', I make it all from scratch and just buy the taco shells (so yes, that may be a little expensive for 6 people unless you get them on special). I use 250g chicken mince, 1 grated zuchinni, 1 grated carrot, 6-8 green parts of the spring onion (I'm not allowed to eat onion), 1/4-1/2 a red capsicum. Fry it all up in a non-stick wok with a little oil first to start the spring onions and heat the spices (use cumin, cinnamon, paprika, chilli, salt). And that's it. Now you build the tacos with lettuce, tomatoes, a BIT of cheese, and natural yoghurt. My husband also has some of the taco salsa (but not me of course...onion!)
The principle is the same for many dishes, and carrot, zucchinni, capsicum, spring onions tend to go in EVERYTHING very well. As do spinich or bok choy sometimes (just add it after you've cooked so it doesn't wilt to nothing).
And here's a real easy one for when you don't want to do much: 'pile-ons' as my dad says! And these I did use to make for a family of 6! SImply cook potatoes in their skins (microwave is quick), split them open and 'pile -on' the toppings (tuna, or bacon, or cooked chicken, a little cheese, and loads of veg - cucumber, lettuce, capsicum, tomato, corn, spring onions or chives, grated carrot, avacado, etc). It's also easy for people to eat 'hearty' and others to eat a smaller potato (or half) and load up on the salad for a 'lighter' meal. For dressing, use lemon, or mayonaise, or natural yoghurt.
For winter, soups are another awesome happy tummy filler - with lots of bread to fill teenage boy bottomless pits. I come from a family of 6 and I'm the only girl, so I do find that guys tend to go for the soups that include meat. ANd these cuts are REALLY cheap, as you cook them for 2-3hrs so the meat just melts off the bone. If you cook from scratch, and include bones (eg a whole chicken if it is chicken soup), the soup is really tasty, and has great nutritional benefit from the cartilege. Just scrape off the meat at end of cooking time and plop it all back in the pot minus the bones (or serve the meaty bones with the soup...we always liked getting stuck in to a hunk of something as kids and sucking out the marrow!). You can easily bulk up the soup too, so it is thick and hearty, with things like pasta, rice, barley or legumes. And of course, soups always have loads of veg - again, add the different veg at appropriate times so that none are overcooked. A dollop of natural yogurt on top and a sprinkle of chives is also a nice finish!
We're having tuna mornay tonight - about 7 types of veg in that one. I also serve mine on a large bed of baby spinach and just a small portion of brown rice as a 'lighter' version. Oh, and don't be afraid of milk in a weight-loss diet - there's more and more research to show that getting your 3 full cups of diary every day PROMOTES fat loss significantly. Calories are NOT equal.
Good luck, hope that gives some ideas...