Homecoming?

my class has to host homecoming this year and being as ignorant as possible they chose space as our theme.. any ideas of what we could have to make this a good dance? that is cheap? We are having it in our gym like it is every year and the main lights are going to be off and it is going to be lighted by other lights.. hard to describe. But we need a good hook to get people to come. also we do not have that much money so expensive things are out… but feel free to put them if it puts a smile on your face!.......