Once time is up, have each team set their pumpkins on the porch with candles illuminating their designs. Once all of the pumpkins are set up, have the judges come out and rate them. The judges can pick their favorite based on humor or actual artistic ability. As a prize, let the winners pick one of their favorite decorations from your party. (They don't have to know they only cost a dollar!)
Have a time limit for the party. Don't cut it short or anything! Just make sure people leave at a reasonable hour. Remember, in the morning, you'll be the one that has to clean up all of the decorations, any trash, and any pumpkin guts that accidentally made it onto your floor. Try to have a big trash bin in your house so that people recognize where to throw away garbage and use it.
Finally, be open to suggestions from others for this party! You don't have to go by the book on planning parties; you want to make them fun, not all structure. If someone else has an idea, let them throw it into the ring. Halloween should be a fun time with your friends, not a chore that you feel obligated to do. I hope these suggestions will help you to plan a fun, easy, and cheap Halloween party that your friends will enjoy!