I got all of my ideas on the website Pinterest, just make an account (free) and start looking. They give you ideas how to make do it yourself decorations, etc. I suggest looking on there!
I would get all decoration, paper plates and such at a dollar store. They do have some cute stuff. For the food I would make it pot luck and ask everyone to bring a dish to share. Or you could do like a taco bar. You provide the meat, and ask people to bring toppings and condiments.