Here is my ghostbusters costume from last Halloween! I did the proton pack in three days.
Step 1: Cardboard!!!
I usually try to make things as easy as I can. So to go with this I went with CARDBOARD!!! Its cheap and easy to cut and bend. I bought two cardboard presentation boards (the ones you used in science class) from a local store.
Hot glue gun
Two bags of glue sticks
Gorilla tape is also a must!!
Along with spray paint (black)
Also chemical lights (get blue and green ones)
Find tubing from a hardware store, the stuff I found was for organizing cables behind a TV.