I would make 12 pounds IF it is a side dish, or about 35 pounds if it is the main dish.
Found this great recipe. It will give you an idea of how much mac and how much cheese.
Bake macaroni and cheese at 350°, uncovered in the center of the oven for about 45 to 50 minutes, or until macaroni and cheese is set.
How much should I feed my dog or, how much should you feed your dog
For a side dish I'd say about 8
The cost of a macaroni and cheese casserole can vary widely depending on the ingredients used and portion sizes. On average, making a homemade macaroni and cheese casserole might range from $10 to $20 for a standard recipe serving 6-8 people. If purchased from a restaurant or catering service, prices can be higher, typically ranging from $25 to $50 for a similar size. Local grocery prices and specific ingredient choices can also influence the overall cost.
Depending on what other foods you are offering I think 3 large cheese balls should be enough.
To make a large cheesy potatoe casserole for 150 people I would use between 50 and 60 pounds of potatoes which would be about 180 individual potatoes or five to six ten pound bags of potatoes.
About 50 cents
50
50
Depends of course. If you buy bargain boxes at the store from $.50 to $3.99. If you make it from scratch considerably more because you use a variety of cheeses, butter, milk and macaroni. My personal recipe is about $10 for 8-10 servings of 3/4 to one cup each.
It requires 50 pounds of feed to produce a hundred eggs