14-18 year olds are huge eaters and these days many are quite strict about what they will eat, especially gluten free and/or vegetarian. In addition, avoid pork, as there are many people who prefer not to eat it.

On the spaghetti page,
www.ellenskitchen.com/bigpots/plan/sphagetti.html
there is a recipe "Baked Sausage Mozzarella Supper for a Crowd".

For this event, I would do 6 times that recipe (allows for teen appetites) with the following changes:
One recipe, use a gluten free pasta and omit the meat. Substitute either vegetarian meatless crumbles or ricotta cheese, same weight. Label one serving line as gluten-free and vegetarian and serve only this recipe there.
For the five regular recipes, sub turkey Italian sausage for pork.

Add salad (see the plan for 100 page for quantities). Allow 14 pounds of good rolls/bread and 3 pounds of butter per 100.

Have a generous dessert. See the dessert planning page for amounts. Use the beverage planning page for beverages

I can't price this for you, as prices vary by region and supplier. Now that you have amounts, you can get a good estimate yourself.