(How did I miss this thread the first time around?!!?!)A lot of folks have suggested the good 'ol mac & cheese, but don't count on that unless you want to gain weight! Refined processed foods are cheap and they taste good but they are oh so bad for you!
If you have a Crock Pot - dried beans are WAY cheap, last a long time, and are good for you. Throw in a packet of Lipton onion soup mix (also cheap) and you've got a healthy nutritious meal. Make a bunch and freeze it.
I find myself always having plenty to eat - it's string money I have trouble with......