Wow, I don't think I could buy enough meat alone for 20 people for under $10. One pound of hamburger for 20 people? We eat that much with four adults and two kids in one meal. But if I had to, I would probably make a huge pot of chili and stretch it with a lot of beans.
2 lbs. ground beef = $3.98
4 cans beans (kidney, black, red, whatever) at 2/$1 = $2
tomatoes and peppers from garden - no cost
onions = $.50
cornbread - normally I would make from scratch, but if we have to buy everything, I would buy the Jiffy mixes, 2/$1 - three batches = $1.50
I don't know what else is needed for the mixes - maybe eggs/water? I'll throw in another $.25 for eggs
seasonings - chili powder, cumin, garlic powder
Two generic bottles of soda = $1.50
Water
$9.73 total
If 20 people are showing up at my house with only a few hours notice, at least one of them ought to be bringing dessert!
