Hot sauce goes a long way with noodles. I'm more of a ramen than spaghetti guy, so i'll drop an egg in there, scallions, etc, pretend it's pho. Trader Joes has pre cooked shrimp, pretty cheap for a bag, just toss a few in there as well.
Mixing chili (or chili beans) with mac and cheese is pretty good, and cheap. And if you're vegetarian you can get the veggie chili and it's all the same. If you've ever been in the military I know you have love for chilimac.