I usually do a search for "cheap party food" or "cheap food for a crowd". lots of great recipes/suggestions out there.
One time I did a steak dinner for about 20 people that didn't cost me very much. I bought a cheap cut of steak on sale. With a yummy marinade and careful grilling, it turned out delish. And my guests felt pampered. (keep in mind that I live in a "blue collar" city and none of my friends expect fancy foodie things. They were just happy since it is very rare to be served steak in someone else's home).
Other ideas:
- Potato based dishes are cheap and filling and a great way to stretch a meal.
- Chicken quarters are one of the cheapest meats that are easy to cook for a crowd and "look large".
- Pans of pasta are cheap. Although I don't always like the presentation so I don't do them very frequently.
- popcorn/kettle corn is a great idea. Dirt cheap, feeds a lot of people, and everyone loves popcorn
I find the main thing is to be willing to be creative, see what's on sale, and constantly keep an eye on the costs. I mentally add up the total of all the ingredients for each dish and that keeps me in check. It's easy to spend more when you are not paying attention (i.e. oh yeah, I need a $3.49 can of pie filling for that dessert that I forgot about and didn't buy on sale). I can often host large parties for very little. One time I had over a dozen people I had to feed for an entire day (lunch, snacks, dinner) and I didn't want it to look cheap or meager. I ended up doing it really inexpensively while making sure there was an overflowing abundance of food and I was very pleased.
Around here, my friends consider $10-$15 "normal" to spend on a potluck dish. I try to keep my dishes around $5 simply by being careful about my ingredients and what I choose to bring. I'm not going to bring (or serve in my home) something that looks miserable - but a fabulous batch of made-from-scratch cream puffs that cost me well under $5 is just as appreciated as an expensive $15 cheesecake.