Here is my advice for the easiest and least expensive Halloween party decorating.
All that you need to do is take a trip to you own linen closet and then a dollar store.
1) White bed sheets- Remove all the accessories from the room (i.e., only keep the main pieces of furniture in the room) and drape all the furniture pieces with your white bed sheets. Allow the sheets to pool on the floor around the furniture.
2) Faux "cob-webs"- Stretch the dollar store "cob-webbing" around each of your pictures, mirrors and anything else stationary in the room.
3) Spiders- Place dollar store, plastic, black spiders in groups around the room. For the best effect, place them on top of the white white sheets.
4) Mice silhouettes- Print off the free online mice silhouettes and place them on the baseboards and stairs around you house.