Do you often pass up the delicious Deli Salads at the super market because of the high price? The Deli salads usually have a lot of sauce and seasonings and they can handle a little diluting with your filler ingredients. This makes the recipe go farther serving more people, and is probably a little healthier too.
If you buy a 1# container when it is on sale, then you can doctor it up by adding extra pasta, potatoes, or whatever veggies or rice you have on hand or left over. I have done this successfully with Deli Potato Salads, Chicken Salads, Pasta Tuna Salads and others. Get creative.
Deli salads are still a more costly convenience, but by stretching them with a little of your own home ingredients you can combine convenience and frugality with added speed and health, not compromising on taste.